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Abstract

The advent of massive amounts of textual, audio, and visual data has spurred the development of econometric methodology to transform qualitative sentiment data into quantitative sentiment variables, and to use those variables in an econometric analysis of the relationships between sentiment and other variables. We survey this emerging research field and refer to it as sentometrics, which is a portmanteau of sentiment and econometrics. We provide a synthesis of the relevant methodological approaches, illustrate with empirical results, and discuss useful software.
Econometrics Meets Sentiment:
An Overview of Methodology and Applications?
Andres Algabaa,b, David Ardiac, Keven Bluteaud,a, Samuel Bormsd,a,
, Kris Boudtb,a,e
aFaculty of Social Sciences & Solvay Business School, Vrije Universiteit Brussel, Belgium
bDepartment of Economics, Universiteit Gent, Belgium
cDepartment of Decision Sciences, HEC Montr´eal, Canada
dInstitute of Financial Analysis, University of Neuchˆatel, Switzerland
eSchool of Business and Economics, Vrije Universiteit Amsterdam, the Netherlands
Abstract
The advent of massive amounts of textual, audio, and visual data has spurred the devel-
opment of econometric methodology to transform qualitative sentiment data into quan-
titative sentiment variables, and to use those variables in an econometric analysis of the
relationships between sentiment and other variables. We survey this emerging research
field and refer to it as sentometrics, which is a portmanteau of sentiment and economet-
rics. We provide a synthesis of the relevant methodological approaches, illustrate with
empirical results, and discuss useful software.
Keywords: Qualitative data; Sentiment analysis; Sentometrics; Survey; Textual analysis
?We thank the Associate Editors (Les Oxley and Stelios Bekiros) and two anonymous Referees,
seminar participants at Ca’ Foscari University of Venice, the European Commission JRC Ispra “Big
Data and Forecasting Workshop” (Ispra, 2019), Ghent University, HEC Montr´eal, the International
Conference on Computational and Financial Econometrics (London, 2019), Skema Business School,
University of Delaware, and Vrije Universiteit Brussel for their useful comments. We are also grate-
ful to Francesco Audrino, Leopoldo Catania, Maxime De Bruyn, William Doehler, Nitish Sinha, and
Leif Anders Thorsrud for stimulating discussions and feedback. This project benefited from finan-
cial support from Innoviris (https://innoviris.brussels), IVADO (https://ivado.ca), swissuni-
versities (https://www.swissuniversities.ch), and the Swiss National Science Foundation (http:
//www.snf.ch, grants #179281 and #191730).
Corresponding author: Samuel Borms, Rue A.-L. Breguet 2, 2000 Neuchˆatel, Switzerland.
Email addresses: andres.algaba@vub.be (Andres Algaba), david.ardia@hec.ca (David Ardia),
keven.bluteau@unine.ch (Keven Bluteau), samuel.borms@unine.ch (Samuel Borms),
kris.boudt@ugent.be (Kris Boudt)
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1. Introduction
There is a long-standing tradition of using sentiment as either a parameter or a variable
in econometric modeling. Historically, the use of questionnaires and proxies to quantify
sentiment variables has been predominant. In recent years, it has become popular to
analyze the sentiment embedded in textual, audio, and visual data. Such data are becom-
ing increasingly available in large amounts thanks to the digitization of communication
media. These media are carriers of potentially interesting information useful for economic
analysis. This has spurred a new strand of econometric research that investigates the
transformation of large volumes of qualitative sentiment data into quantitative sentiment
variables, and their subsequent application in an econometric analysis of the relationships
between sentiment and other variables. We refer to this emerging field as sentometrics,
which is a portmanteau of sentiment and econometrics.
In this survey, we overview the methodology and applications related to an economet-
ric analysis of sentiment extracted from qualitative data. We first define sentiment as the
disposition of an entity toward an entity, expressed via a certain medium. Examples of
entities include individuals, news media, companies, government associations, industries,
and markets. This disposition can be conveyed numerically but is primarily expressed
qualitatively through text, audio, and visual media. Sentometrics studies the computa-
tion of sentiment from any type of qualitative data, the evolution of sentiment, and the
application of sentiment in an economic analysis using econometric methods. Many ap-
proaches already exist for using econometrics with textual data, as recently overviewed
by Gentzkow et al. (2019a), but our focus on qualitative sentiment data is unique. The
overview by Lewis and Young (2019) is limited to the most important analytical ap-
proaches for analyzing textual content in accounting and finance.
The goal of our survey is to provide a synthesis of the relevant work that serves as
a gateway for researchers in econom(etr)ics, finance, and machine learning interested in
the analysis of qualitative sentiment data. The survey takes a hands-on approach by
synthesizing the research around the common challenges. The first critical step is the
clarification of the problem that one is trying to solve. In function of the question,
one collects, prepares, and selects the different data. The filtered qualitative data are
then transformed into numbers using domain-specific sentiment quantification techniques.
These numbers are next aggregated into meaningful sentiment variables. The different
intermediate aggregation steps involve combinations of sentiment calculation methods, as
well as the use of various within-text, across-text, and across-time aggregation methods.
These variables are used as main input in an econometric model that is set up to solve the
question at hand. An important part of the econometric analysis of qualitative sentiment
data is a continuous validation activity. For each of the above topics, we discuss the
relevant methodological approaches and illustrate with empirical results. We also have a
section that sums up some of the available software to perform each step.
2. Definition of Sentiment
The term “sentiment”is used in many different contexts and research areas, but there
is no established definition. We propose a working definition that encapsulates the most
important characteristics of sentiment from the perspective of a researcher wishing to
transform textual, audio, and visual data into sentiment variables and to apply them in an
economic analysis. We also summarize the literature that highlights other characteristics
and alternative definitions of sentiment.
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2.1. Working Definition
We propose the following generic definition of sentiment:
Sentiment is the disposition of an entity toward an entity,
expressed via a certain medium.
This working definition of sentiment embeds three components. First, the expression by
an entity of a disposition in the form of verbal or nonverbal communication. To observe
the private state of mind of any entity, one has to look at their subjective expressions
through both qualitative sentiment data such as textual, audio, and visual data, as well as
numeric data such as quantitative survey data and stock market data. The combined use
of different sources of qualitative sentiment data is called multimodal sentiment, compared
to the use of one data source, which is referred to as unimodal sentiment. Not many studies
have assessed the added value of multimodal sentiment, but in general, findings confirm
an increased level of accuracy over unimodal sentiment (see, for example, Soleymani et al.,
2017). Despite the fact that there are differences between, for example, the expression
of emotion and sentiment (or other human subjective terms), it is not necessarily in the
interest of a researcher interested in sentiment to make this distinction explicit. Second,
the disposition has a measurable polarity or semantic orientation that shows through the
medium of expression. It reveals the direction and intensity of the subjective expression,
on a discrete or a continuous scale. Many definitions simply use positive or negative to
indicate semantic orientation, but application-specific terminologies, such as bullish and
bearish (Antweiler and Frank,2004), dovish and hawkish (Picault and Renault,2017),
or Democrat and Republican (Gentzkow and Shapiro,2010), can be helpful. Sentiment
is usually asserted at different levels of granularity (e.g. a sentence, an entire article, a
sequence of sounds, or an image). Third, the sentiment is oriented toward (an aspect of)
another entity, or exceptionally the expressing entity itself.
This general synthesis encompasses a broad range of different sentiment definitions that
are currently used in the field of economics. Casey and Owen (2013) describe consumer
confidence as the consumer expectations about the future state of the economy. Ludvigson
(2004) notes that surveys are most often used to measure consumer confidence. De Long
et al. (1990) define investor sentiment as a belief about future cash flows and investment
risks that is not justified by the fundamentals. Baker and Wurgler (2007) list several
mediums through which this investor disposition is expressed. Notable examples include
the use of investor surveys, proxies for investor mood changing variables such as the
number of hours of daylight, and the analysis of market data such as trading volume,
implied volatility, mutual fund flows, the premium on dividend-paying firms and the
closed-fund discount. In a survey on sentiment in finance, Kearney and Liu (2014) argue
there are two types of sentiment—namely, investor sentiment, which includes only the
subjective judgments and behavioral characteristics of investors, and text-based or textual
sentiment, which may also contain a more objective reflection of the conditions of a certain
entity. Kr¨
aussl and Mirgorodskaya (2017) hypothesize that media sentiment translates
into investor sentiment. Moreover, Chang et al. (2015) say sentiment affects the formation
of investors’ beliefs and thereby their reactions to information shocks.
In the remainder of the paper, we focus on the use of qualitative sentiment data as
the medium through which the sentiment is expressed.
2.2. Other Definitions
From a psychological viewpoint, Munezero et al. (2014) state that sentiment is one
of the so-called human subjectivity terms that reflects a person’s desires, beliefs, and
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feelings. These human subjectivity terms are features of a person’s private state of mind
that can only be observed through textual, audio, or visual communication. For instance,
the tonality of one’s voice, or the frequency and length of pauses are informative about
underlying sentiment. The same holds for pitch, facial and bodily gestures, the word
use in a written article, and the colors present in a picture. Other human subjectivity
terms include affect, feeling, emotion, and opinion. While Munezero et al. (2014) argue
that there are some notable differences, these terms are mostly used interchangeably in
different strands of the literature. For instance, the distinction that sentiment involves
enduring emotional dispositions toward an object, whereas emotions are briefer, is not of
direct interest for most economic applications. Based on social theory, Evans and Aceves
(2016) classify sentiment as a human state that reflects its condition at a given time and
place. Other states include preference, uncertainty, and ideology, among others.
Taboada (2016) details linguistic sentiment as the expression of subjectivity either
as a positive or as a negative opinion through language. Soleymani et al. (2017) define
sentiment as a long-term disposition with a certain polarity toward an entity. From a
text mining perspective, Taboada et al. (2011) treat sentiment as equivalent to semantic
orientation, containing an evaluative factor (i.e. positive or negative) and a corresponding
strength. In a survey on sentiment analysis, Liu (2015) makes no distinction between
sentiment and opinion and defines an opinion as a quintuple of (1) the expressed sentiment,
(2) the entity toward which it is expressed, (3) the particular (aspect of the) entity that
is mentioned, (4) the opinion holder, and (5) a time stamp. This definition is closest
to ours. Van de Kauter et al. (2015) distinguish between explicit sentiment (conveying
subjective private states) and implicit sentiment (conveying factual information). Shapiro
et al. (2018) deploy a characterization of emotions along the two dimensions valence (how
positive) and arousal (how charged). The valence of word-of-mouth in marketing research
is referred to by Gelper et al. (2018) as a discrete or continuous metric that captures the
attitudes toward a brand. Additionally, sentiment can be looked at from the perspective of
the sender (e.g. the sentiment attached by the author of a text), and from the perspective
of the receiver (e.g. the sentiment perceived by the average reader).
In their analysis of political sentiment, Grimmer and Stewart (2013) use both the terms
“sentiment” and “tone.” They determine tone based on whether information is conveyed
positively or negatively. Tone is more often used in the accounting and finance literature.
Bajo and Raimondo (2017) characterize tone of news as a combination of the degree
of positiveness, negativeness, and uncertainty. Feldman et al. (2010) define tone as the
optimism or pessimism of the information embedded in qualitative verbal disclosures.
Henry (2008) defines tone in earnings press releases as the affect of a communication. In
the construction of a news-based coincident index of business cycles, Thorsrud (2020) uses
tone as a synonym for sentiment and identifies it by determining whether news articles
are positive or negative. In this survey, we also treat tone as a synonym for sentiment.
3. Problem Definition
Sentiment data have the potential to help solve or understand many problems involving
the use of econometrics, across the fields of economics, finance, accounting, marketing,
psychology, and computer science, among others. The adequate choice of methods to
analyze sentiment data depends on the goal of the analysis. A common ground for econo-
metrics applied to sentiment analysis is that one first needs to measure sentiment. Below,
we discuss the use of qualitative sentiment data in applied economic theory and as an
information source in nowcasting and forecasting economic variables.
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3.1. The Role of Qualitative Sentiment Data in Applied Economic Theory
At least since the work of Keynes (1936), economists have been wondering what role
sentiment plays in influencing economic decision making. Understanding the relationship
between sentiment data and decision making at the micro, and macro level is still im-
portant in economic theory. Sentiment can be considered either to contain fundamental
information in the news sense or to capture irrationality up to“animal spirits” in the noise
sense. Both types of shocks move economic expectations and market outcomes at different
horizons (Angeletos et al.,2018). The challenge according to Angeletos and La’O (2013)
is that economists first have to model and then to quantify the sentiment forces behind
the formation of market expectations. They develop an economic theory that does not
depart from rationality but rather connects market expectations with market outcomes
through external shocks they call sentiments. Barsky and Sims (2012) create a dynamic
stochastic general equilibrium (DSGE) model that accommodates both the information
and animal spirits view of confidence. They find most empirical evidence for the perspec-
tive that innovations in confidence reflect information about future economic prospects.
One explanation for the importance of economic sentiment is that it acts frequently as a
self-fulfilling prophecy (see Petropoulos Petalas et al.,2017 and the references therein).
When there is consumer or business pessimism about economic growth, actual negative
growth can be a direct consequence of it. A more specific example is bank runs. When too
many depositors’ sentiment about other depositors is negative, the unwanted outcome, a
bank run, is more likely to materialize (Diamond and Dybvig,1983).
In this regard, sentiment indices based on qualitative data can provide a more direct
data-driven instrument to assess various types of economic shocks, or proxy for matters
such as confidence or expectations. Larsen and Thorsrud (2019) use structural vector
autoregression to identify news and noise shocks in a panel of text-based measures and
other economic variables.
Sentiment proxies provide a way to test behavioral hypotheses on the aggregate level
or on the individual level. In general, the key questions pondered in a behavioral anal-
ysis are “What drives sentiment?” and “What is the behavioral impact of the sentiment
transmitted?” An example of a behavioral hypothesis is whether entities inflate the tone
in their written communication to influence market reactions. Both Picault and Renault
(2017) (for the European Central Bank) and Arslan-Ayaydin et al. (2016) (for firms) val-
idate this hypothesis. Sentiment in texts can be argued to be driven by a self-interest
to generate particular external outcomes. In Garz (2014), the evidence shows a strong
bias in terms of the number of negative and positive reports related to unemployment
that is not the consequence of an asymmetric interpretation of the official numbers but
rather associated with noneconomic information and the process of news production itself.
Along these lines, the degree of sentiment involved in images appended to advertisements
can also have clear intentions to impact customer behavior. Kalogeropoulos (2018) stud-
ies the impact of various media outlets on individual economic expectations, not finding
tone to be a good predictor. In the finance literature, behavioral theory predicts that
short-horizon returns are reversed in the long run (Tetlock,2007).
There is a growing concern about the severity and impact of media bias. Closely
related, Flaxman et al. (2016) explain there are two strands of thought about the impact
of improved production, distribution, and discovery of news articles (or generally, any
multimedia). Some defend it increases exposure to diverse perspectives; others argue
that it increases ideological segregation. They find empirical support for both camps,
thus a further investigation of the impact of a biased media production and consumption
5
behavior would be worthwhile.
Boudt and Thewissen (2019) base their analysis of CEO letters on psychological phe-
nomena such as framing (Tversky and Kahneman,1981) and the serial position effect
(Glanzer and Cunitz,1966). These and similar phenomena can also be used to bet-
ter understand the sentiment conclusions. Purely as an illustration, stronger weights of
negative sentiment words in comparison to those of positive sentiment words could be
supported by the negativity bias, claiming that negative things have a greater impact.
It could also be related to the fact that news media tend to emphasize negative news
(e.g. Lowry,2008). The priming, agenda setting, and framing communication theories
described in Scheufele and Tewksbury (2007) can also be subject to more precise testing
using multimodal sentiment measures.
Many different entities can have sentiment attributed from different data sources.
Sentiment across these different entities tends to interact in particular ways, possibly in
a contagious manner. The assessment of these sentiment flows, the feedback effects, and
the associated information dispersion over time concern a network analysis of sentiment.
The Global Database of Events, Language, and Tone (GDELT) project1is the most
comprehensive effort to date of a global network analysis of events and related sentiment.
These data and social media data are useful to analyze what network structures would
mitigate behavioral misperceptions, a question brought up by Teoh (2018).
Larsen and Thorsrud (2018) use a graphical Granger causality modeling framework
to gain insights into the network of economically relevant news topics. Every node in the
graph represents a sentiment/topic time series. The graph can be used to detect which
narratives dominate and what the degree of news spillover is—that is, what news stories
from which countries Granger cause the occurrence of any other news stories.
Eshbaugh-Soha (2010) emphasizes the role news coverage and tone can have on gov-
ernment trust and how it is central to explaining effective leadership. News provides
country leaders a means to communicate their messages, but the local perception can
differ significantly. Therefore, an interesting study would be to assess the spread between
the sentiment of news reported in one region and the sentiment of similar news reported
in another region.
3.2. Measuring, Nowcasting, and Forecasting of and with Sentiment
Sentiment time series indices aim to reflect the evolution of sentiment over time. A
well-known text-based example is the Economic Policy Uncertainty (EPU) index of Baker
et al. (2016).2This index measures uncertainty, a specific type of sentiment. Manela
and Moreira (2017) create a news-based measure of option-implied uncertainty, arguing
it incorporates disaster concerns expressed via the media. In many other applications,
sentiment is also considered an explicit or implicit proxy for a certain desired output,
such as for the visualization of company reputation (Saleiro et al.,2017).
We refer to quantifying already observed sentiment as sentiment measurement, while
the prediction of the unobserved current and future sentiment is called sentiment now-
casting and forecasting, respectively. Sentiment is a latent variable, meaning it is not
readily observable. Measuring sentiment is a key task in any sentiment-based analysis.
1See https://www.gdeltproject.org.
2The EPU index for various countries can be retrieved from: http://www.policyuncertainty.
com. The online publication of text-based indices is becoming prevalent, see also: https://www.
retriever-info.com/fni.
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In the now- and forecasting literature, sentiment measures are considered a timely
driver of other variables. There are three approaches to the type of sentiment that is
used. Sentiment is proxied using available (questionnaire-based) indices, sentiment is
constructed itself from a qualitative data source commonly using relatively simple meth-
ods, or sentiment is bought from a data provider such as Reuters (e.g. Thomson Reuters
MarketPsych Indices) who in general uses a more complex methodology for the compu-
tation. The obtained sentiment is then transformed for usage in prediction models, to
obtain the best possible prediction at any time. Sentiment variables are rarely used alone
as explanatory variables but are usually added to a set of standard explanatory variables
to see whether its integration improves or deteriorates forecasting performance.
The integration of sentiment has indeed already shown its capacity to improve fore-
casting performance. A significant impact of sentiment expressed through diverse media
on stock returns and trading volume is found by Heston and Sinha (2017), Jegadeesh and
Wu (2013), Tetlock et al. (2008), Tetlock (2007), and Antweiler and Frank (2004). Ardia
et al. (2019b) incorporate textual sentiment time series into the long-term forecasting of
the U.S. industrial production growth rate using sparse regression techniques.
Beyond improved predictions, using sentiment data is very flexible and timely, espe-
cially compared to traditional sentiment extraction methods such as surveys. Changes in
sentiment methodology can easily be backtested using the available data. Modifying the
structure of a survey, however, necessitates the survey to be sent out again to obtain new
results. Information derived from sentiment data hardly suffers from release lags, making
timely sentiment an ideal variable to enhance nowcasting models and consequently to
craft timelier policy responses.
As in Hamilton et al. (2016), sentiment analysis on word level can be used to measure
the time-varying perception surrounding certain words. For instance, “terrific” had a
negative connotation up to 1960, but then became more positive. Lukeˇs and Søgaard
(2018) find that words predictive of sentiment at one point in time remain not necessarily
equally predictive at a later point, and that models trained on old data perform worse
than models trained on recent data. They suggest a predictive feature selection approach
to deal with temporal polarity shifts. The implication of changes in language over time
is that the methods of sentiment quantification should evolve with it.
It is becoming well established in economics and finance that adding soft (qualitative)
information on top of hard (quantitative) information results in predictive information
gains. However, the soft information is usually explored through textual content. Audio
and visual content have been explored less so but may deliver additional information value,
according to Mayew and Venkatachalam (2012), who find that vocal cues of managers
during conference calls predict a firm’s future performance.
4. Qualitative Sentiment Data
The various ways in which economic agents express their sentiment leads to textual,
audio, and visual sentiment data. Sentiment data are short for “sentiment-bearing” data.
Most of the examples and methods in the remainder of this survey focus on textual data,
because audio, and visual sentiment analysis is still in its infancy (Soleymani et al.,2017).
Teoh (2018) does so similarly but acknowledges the rising relevance of audio, and visual
data. Currently, the main focus of current research in sentometrics effectively lies with
textual data due to their wide availability in the digital form of news media articles,
company filings, or social media posts (see e.g. Loughran and McDonald,2016).
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The choice for textual data thus comes from the fact that most research and appli-
cations have been developed for this type of data. An advantage of focusing on texts is
that many other forms of unstructured data can be transformed into textual data and
then analyzed as if they were textual. For instance, audio data are often transcribed into
textual data and can thus be analyzed using tools from this domain.
Multimodal sentiment analysis techniques are expected to gain importance due to the
internet, which has become more of a widespread multimedia platform. Where possible,
we highlight close relations between the analysis of textual data and the analysis of audio,
and visual data, covering potential similarities from one data type approach to the other.
Doing so, we outline a uniform high-level framework that is applicable to all these data
sources. The concepts of feature extraction, quantification, aggregation, modeling, and
validation are very much transferable, though almost never presented as such.
4.1. Information Sources
The information sources for sentiment analysis in econometrics can be grouped in two
ways. First, it can represent where the data were published. This includes news outlets (a
journal, a social media channel, YouTube, a vlog, or a blog), companies and governments
(regarding the publication of an official press release or an official report), or publication
venues (an academic journal or a book publisher), among others. The source in this
context should not be confused with the actual expresser of the sentiment; for instance,
the source can be a journal, and the expresser a company or one of its top managers.
Second, it can represent from where the data were retrieved. The largest worldwide
textual data providers are LexisNexis, Dow Jones’ Factiva, and Reuters. Access to these
databases is paid. A cheaper alternative, if allowed, is to scrape textual data from the
web. A specific scraping procedure needs to be set up, which is a cumbersome activity, and
in general goes with a considerable degree of hit-and-miss in terms of texts successfully
collected. There also circulate some freely available data sets—for instance, the eight text
data sets analyzed by Zhang et al. (2015) or the list of freely available text data sets
provided by Ravi and Ravi (2015).3
The acquisition of the data requires a good data management system, able to struc-
turally store many gigabytes, such as MySQL. The database should also have fast query
functionalities, for example delivered by technologies such as Solr or Elasticsearch.
4.2. Alternative Sentiment Variables
Instead of the algorithmic extraction of sentiment from data, sentiment is also often
proxied by asking people through surveys. The U.S. Consumer Confidence Index or
the European Economic Sentiment Indicator are actively monitored examples of indices
based on surveys (see for instance the analyses of Ludvigson,2004 and Gelper and Croux,
2010). However, surveys have the downside of being costly, are hard to replicate, have a
publication lag and cannot be backtested. Both survey-based measures and data-based
measures have their value, and are in many cases complementary. Ardia et al. (2019b)
show that the specification that includes both time series measures generates the best out-
of-sample predictive power. Baker and Wurgler (2006) derive a sentiment index through
a principal component procedure from six sentiment proxies proposed in the literature,
without going through any sentiment quantification process themselves.
3A collection of open-source textual, audio, and visual data can be found at https://pathmind.com/
wiki/open-datasets.
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Similar to textual data providers, there exist a number of textual sentiment data
providers. Two often-used solutions are the series from RavenPack, and the Refinitiv
(formerly Thomson Reuters) MarketPsych Indices.
4.3. Data Limitations
A first limitation concerns data availability and the disagreement between textual
databases. Ridout et al. (2012) find preliminary evidence that there are stories (in their
study mostly international coverage) from printed newspapers that are systematically
missing in electronic databases. Thus, not only do texts need to be collected, but the
content from multiple sources also needs to be aggregated neatly. Chiou and Tucker (2017)
cover some of the likely issues of content aggregation. The problem of data availability
and data disagreement is small for open government databases, such as accounting textual
data (e.g. EDGAR), court decisions (e.g. PACER), or patents (e.g. Espacenet). Much in
the same way Riffe et al. (2019) note that the universe of online posts is “unlimited and
unknowable and inherently unstable over time,” the problem becomes more persistent for
data coming from corporate resources, news media, or social media. Any sample drawn
from that data might not be representative due to nonrandom sampling; true probability
sampling is hard in the context of big data. Lacy et al. (2015) mention convenience
sampling (a sample primarily defined by availability) and purposive sampling (a sample
primarily defined by the nature of a research undertaking) as common practices.
An important aspect in data collection is the notion of data vintages. In a real-time
setting, a researcher uses the data available at a given time, called a vintage or a snapshot.
Yet, many data are subject to revisions. For instance, most data used in macroeconomics
are updated one or more times until final numbers are reached (Croushore and Stark,
2003). The compilation of the FRED-MD historical vintage database of macroeconomic
indicators was a response to this problematic (McCracken and Ng,2016). This same
difficulty persists in textual data, particularly with online publication and social media,
with the data frequently updated, revised, or even removed from the information outlets.
Saltzis (2012) reveals in a sample of breaking news stories on six major U.K. online news
sites that the stories were updated on average 5.7 times. As such, the traditional process of
scraping websites for historical news may lead to a forward-looking bias since the retrieved
news will typically be the latest version of the news articles and not the one at the time
of first publication. This phenomenon is crucial to deal with in intraday studies.
The problems described above lead to issues of reproducibility and limitations to gen-
eralizability of results.
5. Preprocessing, Enrichment, and Selection of Qualitative Sentiment Data
Textual, audio, or visual data rarely arrive in a format that is ready for input into
an algorithm. The data typically start off being very unstructured, and through a se-
quence of steps structure is imposed to make the data ready for further analysis. We
define restructuring as doing two things: preprocessing and enriching the data. Both the
preprocessing and metadata enrichment ideally come before the actual data selection to
have the most information available to do an optimal filtering.
5.1. Restructuring Textual Data
In this subsection, we describe the preprocessing and metadata generation concerning
textual data. Bholat et al. (2015) provide a useful summary of many relevant text mining
techniques for preprocessing and data enhancement.
9
5.1.1. Preprocessing
Raw textual data often come in a JSON or an XML file from which the actual text
needs to be extracted first. This process is called parsing. Depending on the type of
data available, this can be a relatively straightforward or tedious task. As part of this
process, remaining garbage such as HTML tags, addresses, or other formatting is removed,
or simply not selected through the parsing algorithm.
Furthermore, textual data are inherently (ultra)high-dimensional (Kelly et al.,2019).
Gentzkow et al. (2019a) highlight that to structure a text with a length of wwords, each
of which is drawn from a vocabulary of qpossible words, the unique representations of
this text has dimension qw. Moreover, all characters in the text are probably not equally
informative in assessing the sentiment of a particular document. For example, stop words
such as “the” are seldom indicative and are usually removed to reduce the noise and the
dimensionality. Some type of further cleaning is often required to deal with issues such as
spelling mistakes or (nonstandard) abbreviations (Nowak and Smith,2017). Denny and
Spirling (2018) outline several common preprocessing steps. The output is a corpus of
cleaned texts.
Textual data comes in various granularities: words, sentences, paragraphs, and whole
articles. Sentiment is the output of a function applied to specific components extracted
from texts, also called terms. The most common kind of components are n-grams, a
sequence of nwords. Breaking up text into n-grams is called tokenization. If n= 1,
tokens are referred to as unigrams. A bag-of-words approach presumes that the relative
order of unigrams is irrelevant, but words are not necessarily independent of each other.
More generally, a bag-of-words can be denoted by bag-of-tokens, where tokens can be any
sequence of words. Further cleaning is needed to drop, for instance, punctuation marks,
or transform all terms into lowercase, stemmed, or lemmatized form.
Terms are summarized into a document-term matrix, with the rows as the documents,
the columns as the terms, and the cells as the values that measure the (weighted) frequency
of occurrence of the terms. A document-term matrix is usually of high dimension and
consequently very sparse, meaning, with a lot of zero entries. In a document-term matrix,
the sparsest features are typically removed.
5.1.2. Metadata Enrichment
A corpus as is consisting of only documents can be enriched by adding all sorts of
metadata. Metadata either already exist or are objective, such as a time stamp, the au-
thor, the news outlet, the language, or the geography. A good case for having metadata is
that textual information is expressed across many different venues, including newspaper
articles, newswires, and social media, all with a possibly differing degree of information
value. Heston and Sinha (2017) emphasize the importance of studying news types to
understand how financial markets process information and when underreaction and over-
reaction in returns occur. Aggregation across a metadata marker gives information about
the sentiment concerning that particular metadata—for example, the sentiment about a
given economic topic.
The available qualitative metadata need to be quantified for further use in the analysis.
This can be done using binary or relevance variables. In the first case, one enumerates all
qualitative metadata across the corpus for a given article and assigns a value of 1 if the
metadata are of importance to that article, and 0 if not. A relevance variable follows the
same principle but assigns a continuous score based on the connectedness of the metadata
to the article. Some metadata lend better to be modeled as a dummy variable (e.g.
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language or geography), others as a relevance variable (e.g. predefined topics). If there
are too many individual instances of the metadata, one can consider to group them. Other
metadata can be generated using text mining models. The first type of metadata that
can be generated are entities, using named entity recognition extraction techniques. The
second type of useful metadata are topics and related keywords based on a supervised or
an unsupervised topic model. The features can be valued as the probability score coming
out of the topic model. Readability of a text (e.g. Loughran and McDonald,2014) or the
tense of a text are two other potentially useful metadata indicators.
5.2. Restructuring Audio and Visual Data
The underlying raw format of audio, and visual data is less comprehensible and vaster
than textual data. One second of a video is size-wise equivalent to at least hundreds of
pages of text; the maxim “An image is worth a thousand words” is no exaggeration. We
emphasize some important aspects about the restructuring of audio, and visual data.
5.2.1. Preprocessing
For sentiment classification, visual and audio data are processed into emotional clues
handy to discriminate between different sentiment categories. A major focus of senti-
ment extraction in visual data is on facial expressions. Secondary are other nonverbal
expressions (e.g. hand gestures) and environmental factors such as what is happening in
the background. There are seven basic emotion classes (danger, sadness, surprise, fear,
disgust, joy, and contempt) that can be inferred using a facial expression coding system
originally proposed by Ekman and Friesen (1976). One can then construct variables that
express the distance between several of these positional facial characteristics.
Visual data can be boiled down to image data. A video in that respect is a collection
of segments, and every segment is a collection of images. Audio data can be boiled down
to textual data using speech-to-text technology complemented with specific audio features
(such as pause duration).
5.2.2. Metadata Enrichment
The principles of metadata enhancement for textual, audio, and visual data are similar,
but the content of the metadata is different. Qualitative metadata such as author or time
of publication are the same. Examples of useful audio features are pitch, pause, laughter,
overlaps, and voice intensity; examples of visual features are color and motion. Videos
have both visual and audio features. Wang et al. (2003) describe features and extraction
techniques across four categories (spatial visual, motion, coding and audio).
A downside of features retrieved from nontextual data is that many of them require
a large-dimensional representation. For a video, a manner to construct a feature called
“smiling”could be to take the number of seconds a person smiles in the video. The decision
of whether a person smiles is a function of various facial characteristic points that should
be mapped deterministically to the binary outcome “smiling” or “not smiling.”
5.3. Selection of the Relevant Data
Following a general-to-specific approach, the original and vast corpus of documents
needs to be trimmed to a subselection of relevant texts. If the selection procedure is too
restrictive, important data may be omitted; however, if irrelevant data are included, it
may drastically lower the signal-to-noise ratio. This can be considered as “querying” the
corpus database to extract the right selection of texts. Querying can be based on a search
of keywords in the database using, for example, a regular expression. It should be made
11
clear beforehand which texts are necessary to include in the analysis, or the selection
can be approached as an optimization problem itself. The latter strategy would require
defining different sets of keywords and finding out which keywords give the best outcome
in terms of an objective (e.g. forecast accuracy).
To model an outcome variable, it is not always needed to focus exclusively on (sen-
timent) measures directly related to that variable. On the contrary, Larsen et al. (2020)
argue that many news topics are, in their case, of interest to form inflation expectations,
thus it would be limiting to only target media mentioning terms related to inflation. Kelly
et al. (2019) tackle the problem of selection simultaneously with modeling a set of ob-
served covariates. They propose a method that only includes phrases of interest when
useful, conditioning on the observed covariates, building on the model of Taddy (2015a).
6. Quantification of Sentiment
Any sentiment measure is a proxy for the actual prevailing sentiment and needs to
be estimated. This can be done by human annotators or by a statistical function. A
wide variety of techniques exist to infer the sentiment embedded in qualitative data, but
measuring sentiment is inherently application- and data-specific. Therefore, it is neither
possible nor recommended to consider sentiment computation in a single manner.
Sentiment is quantified for a given observational data unit—for instance, a text or a
video. Quantification of sentiment is either on a discrete scale (classification into two or
more classes, such as negative, positive, and neutral) or on a continuous scale. Based on
decision rules, one can go from continuous to discrete output. Some methods produce a
tuple of a positive and a negative sentiment (probability) score. Multiple sentiment scores
from one computation method can be considered as separate methods and can turn out
to be more informative.4Sentiment scores might benefit from a normalization for in-
terpretation purposes and possible outlier elimination. Sentiment analysis can also take
up a more fine-grained externalization, called aspect-based sentiment analysis (De Clercq
et al.,2017). This type of sentiment analysis separately measures the sentiment for dif-
ferent aspects and entities mentioned in the data unit. This is a combined problem that
requires the extraction of entities and their aspect terms, classifying the aspect terms,
before doing the sentiment calculation for each of the extracted combinations. One could
draw an analogy with “feature-based opinion summarization” (Hu and Liu,2004), which
is less specific.
6.1. Textual Data
Textual sentiment quantification uses tools from the broad field of natural language
processing (NLP) to quantify the sentiment of a given text. It consists of many NLP-
related subtasks, such as identifying entities and extracting relevant features. We briefly
discuss the lexicon-based and machine learning approaches as the two main types of
methods for sentiment computation. The data unit is usually a document, a paragraph,
or a sentence. Some fields prefer one over the other. Sentiment can be detected more
precisely at sentence level, but in political science, for instance, most often the analysis
remains at document level since it requires less heavy NLP (Grimmer and Stewart,2013).
4For instance, a net textual sentiment value of two can be obtained from both two positive and zero
negative words, or 20 positive and 18 negative words. The number of polarized words can be retained as
separate sentiment scores, else its information can be used for within-unit aggregation.
12
For a broader treatment of textual sentiment computation and associated subtasks, we
refer to Liu (2015) and Ravi and Ravi (2015).
The classification accuracy of the various sentiment approaches varies. Typically, ma-
chine learning algorithms outperform lexicon-based methods out-of-sample, at the expense
of computational efficiency and model transparency. The difference in performance is a
function of the type of texts and the domain specificity of the lexicon employed. Ribeiro
et al. (2016) provide an extensive overview of the accuracy of both lexicon-based and
machine learning–based sentence-level sentiment analysis. They compare 24 popular sen-
timent methods over 18 labeled data sets. Their experiments convey first of all a rather
low average level of accuracy. More importantly, there are large differences in the accuracy
across sentiment methods and across data sets. Their results also reveal no outstanding
method at the sentence level. The conclusion is that a sentiment quantification method
needs to be selected carefully depending on the purpose.
6.1.1. Lexicon-Based Approaches
A lexicon-based computation of sentiment is the most straightforward, efficient, and
parsimonious method. Turney (2002) defines lexicon-based sentiment analysis as “calcu-
lating sentiment for a document from the sentiment of words or phrases in the document.”
Mechanically, this requires the use of a sentiment lexicon with sentiment information about
important (combinations of) words, which is then matched with a text. A lexicon is thus
a collection of pairs of words (or a sequence of words) and associated sentiment scores. In
most cases, lexicons stick to unigrams, but for some applications, it is more effective to
use n-grams. Picault and Renault (2017) construct a lexicon specific to European Central
Bank communication and explicitly consider n-grams, such as the positive bigram “lower
unemployment.” The size of a lexicon ranges on average from in the hundreds to in the
thousands. There is no preferred lexicon size; too large can mean inaccuracy due to noise,
and too small might mean not enough coverage or a lack of important words. Comparing
lexicons is not always easy, given the often varying sizes but also because there is no
universal polarity grading system (Ravi and Ravi,2015).
There is a distinction between general lexicons and domain-specific lexicons. Both
the Henry lexicon (Henry,2008) and the Loughran and McDonald lexicon (Loughran
and McDonald,2011) were developed as a response to the suboptimal applicability of
generic lexicons to texts in the finance domain—for example, earnings press releases. The
Lexicoder Sentiment Dictionary (Young and Soroka,2012) is tailored to news content
about politics. Lexicons are simple and the least black-box solution, and usable at any text
level. However, lexicons can be brittle when facing domain shift and complex syntactic
constructions (T¨
ackstr¨
om and McDonald,2011). Very few lexicons are domain-portable,
meaning applicable across several domains and text structures. It is difficult to achieve,
if it is at all, and therefore hardly desirable.
Liu (2015) sees three broad ways of generating lexicons—namely manually, dictionary
based, and corpus based. An additional approach to building lexicons involves a combi-
nation of manual labor and a statistical methodology, which may arise from the machine
learning literature. It is important to differentiate between machine learning algorithms
for lexicon construction and those algorithms to measure sentiment but with no explicit
intention to obtain a sentiment lexicon. We cover the latter in the next subsection. Apart
from the manual approach, all methods entail automatic processes to varying degrees.
The manual approach to building lexicons has annotators assigning a sentiment score
to selected words. Notable fully hand-curated lexicons are the Stone et al. (1963) General
13
Inquirer and the Bradley and Lang (1999) ANEW word lists. Crowdsourcing platforms
such as Amazon Mechanical Turk have made the task of developing high-quality manual
lexicons more accessible nowadays. To our knowledge, the NRC lexicon of Mohammad
and Turney (2013) was the first to be built using crowdsourcing services.
A dictionary based approach allows producing lexicons more cheaply while keeping
a good level of accuracy. This method starts from a list of seed sentiment words with
known polarity (often found using the manual approach) and then expands this list by
using synonyms and antonyms coming from a large base dictionary. A suitable base
dictionary is the WordNet database (Miller,1995). This lexicon in conjunction with
sentiment seed words was used to produce WordNet-Affect (Strapparava and Valitutti,
2004) and SentiWordNet Baccianella et al. (2010).
The corpus based method adapts an existing lexicon using information from a domain-
specific corpus. The researcher first needs to adjust the sentiment orientation of the words
to the new domain. Second, it may use linguistic rules to include new words in the lexicon.
In this regard, Hatzivassiloglou and McKeown (1997) introduce the notion of sentiment
consistency. For instance, adjectives with a similar sentiment orientation are often used
in groups. Kanayama and Nasukawa (2006) propose the idea of sentiment coherency; the
same sentiment orientation tends to be expressed in consecutive sentences, while sentiment
change is expressed by an adversarial expression (e.g. “but” or “however”).
Statistical methodologies are the fastest and cheapest but the most prone to error.
They typically start from a set of words from a previously built lexicon or a corpus, then a
statistical methodology is used to find the sentiment orientation of those words. Jegadeesh
and Wu (2013) use a regression framework to measure the sensitivity of words (“word
power”) to stock returns; this could then be used to form a finance-specific sentiment
lexicon. Lexicons can also be derived from (Bayesian) regularized methods, such as the
Ridge, the LASSO, or the elastic net regression (see e.g. Nowak and Smith,2017 and
Pr¨
ollochs et al.,2015). Pr¨
ollochs et al. (2015) argue that a shrinkage approach (Ridge
regression) is superior over a variable selection approach (LASSO regression) because
multicollinearity among the token predictors tends to be strong. In the corpus-based
category, Engle et al. (2020) create a climate change vocabulary based on a collection
of climate change white papers and glossaries. Their final lexicon is composed of the
unique stemmed unigrams and bigrams, weighted by their respective term frequency–
inverse document frequency (tf-idf) scores. To create a daily climate change index, instead
of term matching, they use the cosine similarity between the tf-idf scores of a given article
and the scores in the lexicon.
Lexicons do not cope with the linguistic context around which the sentiment words
appear. To this end, advanced lexicon-based methods integrate so-called valence shifters in
the sentiment computation. Common types of valence shifters are amplifiers (e.g. very),
downtoners (e.g. barely), negators (e.g. not), and adversative conjunctions (e.g. but).
These valence shifters act on polarized words in the lexicon in particular ways depending
on how close they appear to these polarized words. Taking the example of negation,
one way to apply it to lexical entries is termed shift negation (Taboada et al.,2011)
as opposed to switch negation.5Having lexicons consisting of n-grams would also allow
disambiguating of word use in different contexts. According to Young and Soroka (2012),
5The importance and application of valence shifters is also a function of the document type. Hutto
and Gilbert (2014) created the VADER sentiment analysis system for social media texts, letting word
shape (e.g. capitalization), slang (e.g. “kinda”), and emoticons, among others, act as valence shifters.
14
even a modest integration of contextual (preprocessing) routines is fruitful. Taboada
(2016) enumerates multiple linguistic insights to account for in sentiment analysis.
Not only domain specificity, but also language specificity is important. Most resources
are still in English (Ravi and Ravi,2015). In practice, one often sticks to translation.
Either one translates the focused text from a resource-poor language into a resource-rich
language (usually English) for which a robust sentiment method (e.g. lexicon) is available,
or one translates an existing word list into the focused language. A third option is to trans-
late annotated corpus resources from a resource-rich language to the focused language and
use these to develop (or improve) another sentiment method. In many circumstances,
however, the performance of translation results in a loss of accuracy. Mohammad et al.
(2016) surprisingly find that, with Arabic social media as the focused texts, sentiment
analysis of automatic English translations is competitive to existing Arabic sentiment
analysis systems. On the other hand, translation made the human annotations become
worse than sentiment analysis, and adding Arabic translations of sentiment-labeled En-
glish tweets data to Arabic training data resulted in a drop in accuracy, due to bad trans-
lations. Translation invariably comes with additional problems to solve. Bannier et al.
(2019) start from the English Loughran and McDonald lexicon by doing word-by-word
translation to German. On top of that, they deal with distinct grammatical features of
the German language related to inflectional and lexical morphology, as well as compound
wording. They claim to have described a comprehensive framework for future adaptations
of dictionaries into other languages. To test the equivalence between their lexicon and the
Loughran and McDonald one across positive, negative, and neutral categories, they rely
on the two-sided equivalence test of Blair and Cole (2002). The test checks for accordance
in terms of the mean number of detected polarity categories, given a confidence interval.
6.1.2. Machine Learning Approaches
The extraction of sentiment as a stand-alone problem is studied by machine learning
and computational linguistics scientists. The purpose is to optimize the measurement
of sentiment based on a learning algorithm typically benchmarked against an annotated
data set of text with corresponding sentiment values. The objective, in this case, is well-
defined and dependent on the type of data source (e.g. product reviews or images) and
the type of sentiment output (e.g. classification into positive or negative). The learning
algorithm identifies the characteristics among the preprocessed smaller pieces of textual
characteristics (i.e. words, n-grams, phrases, counts, and other information) that are most
important in measuring sentiment. A survey of different machine learning algorithms
applicable to text is given in Evans and Aceves (2016). Machine learning can be branched
into supervised and unsupervised learning, both used on many occasions for sentiment
analysis.
Supervised machine learning requires an annotated data set—meaning, a set of doc-
uments with, for every document, a sentiment value, leading to what is often called the
gold standard. Annotation can already exist from the data (e.g. product rating stars),
but, in most cases, is constructed manually. Building such a data set from scratch can be
expensive and time-consuming while also prone to bias. Especially for domain corpora,
annotation can be hard due to possibly complex specific sociolinguistic contexts (Hamil-
ton et al.,2016). The annotation cost also depends on the type of text. Van de Kauter
et al. (2015) review some of the complexities of doing annotation. Taddy (2013a) outlines
a procedure to select from a large corpus the texts that are most useful to annotate.
Determining the best data examples to be labeled is referred to as (pool-based) active
15
learning. Once the tagged data set is obtained, a specific machine learning algorithm
is trained with it. Pang et al. (2002) clarify the sentiment classification problem, and
experiment with the Naive Bayes, maximum entropy classification, and Support Vector
Machine (SVM) learning techniques. Naive Bayes and SVM are essentially text regres-
sions of the sentiment target variable on a large-dimensional space of textual elements,
such as words, which get assigned a weight. More recently, neural networks, primarily due
to the emergence of deep learning, have become more prominent. One can also combine
several learning algorithms. For instance, Das and Chen (2007) employ a majority voting
scheme across five classifiers, claiming it minimizes false positives.
An unsupervised learning approach lets the data decide the categories or representa-
tion by themselves. Any unsupervised method is typically hybrid or semi-supervised, as
there is need for specific minimal inputs from the modeler. A classic example is the sug-
gested approach by Turney (2002), which ranks phrases based on their pointwise mutual
information (PMI) with respect to two seed words, one negative (“poor”) and one positive
(“excellent”). It infers the semantic orientation from the semantic association with respect
to a manual set of seed words. Remus et al. (2010) develop the German SentiWortschatz
dictionary using the PMI approach. A vector space model (VSM) is a more complex un-
dertaking. These models generate word embeddings, which are latent quantitative vector
representations of textual information, such as documents, paragraphs, words, phrases,
and even letters. A VSM learns distributed vector representations that capture many
precise syntactic and semantic word relationships. Words closer to each other in terms
of linguistic context receive a more similar quantitative representation because they are
assumed to share the same semantic meaning.6Global matrix factorization methods (co-
occurrence counts based) and local context window methods (prediction based) are the
two main families for learning word vectors.
Latent semantic analysis (LSA) is a notable example of a global matrix factorization
method. It reduces high-dimensional count vectors to a lower-dimensional latent semantic
vector space. Hofmann (2001) introduces a probabilistic version of LSA, defining the
semantic space over a set of latent variables referred to as “aspects” based on a generative
model for word-to-document co-occurrences. His model allows figuring out, for instance,
which latent aspects are most likely to generate a word, or what the latent class posterior
probabilities are given a certain document and word. Liu et al. (2009) refactor the model
to capture a multidimensional measure of blog sentiment, considering sentiment as a joint
contribution of a few hidden factors. They call their work S-PLSA (sentiment probabilistic
latent semantic analysis). In a subsequent time series regression, they form sentiment
variables as the average sentiment mass attributed to each of the hidden sentiment factors.
Most of the recent research on word embeddings has gravitated toward the prediction-
based method using neural network architectures. The Word2Vec approach of Mikolov
et al. (2013) is one of the earliest and best-known techniques in this category. Word2Vec
uses the continuous bag-of-words (CBOW) or the continuous skip-gram model architec-
ture. In CBOW, one tries to predict the current word in a text from a window of sur-
rounding context words. In contrast, in the skip-gram model, one tries to predict the sur-
rounding context words using the current word. Mikolov et al. (2013) also formalized the
idea of using vector operation, such as vec(“Madrid”)vec(“Spain”)+ vec(“F rance”)
vec(“P aris”). GloVe (Pennington et al.,2014) aims at taking the best of the count-based
6Word embeddings are an advanced way of doing text vectorization, compared to, for instance, the
simpler construction of a document-term matrix.
16
and prediction-based methods, with a first attempt to integrate both global and local
statistics. Pennington et al. (2014) find that the quality of GloVe’s learned representa-
tions is slightly better than Word2Vec’s vectors, but it depends on the task at hand. A
more recent method is fastText (Bojanowski et al.,2017). It incorporates subword in-
formation into the learning process such that words not observed in the training corpus
(out-of-vocabulary) can still be assigned a word vector. The current state of the art in
word embeddings are the deep neural network Bidirectional Encoder Representations from
Transformers (BERT) models and its variants (Devlin et al.,2018). These models most
explicitly integrate global and local context. For example, the word vector for “right” in
“I am right” and “I take a right turn” will be different.
Estimated word embeddings are used as an input to more traditional sentiment classi-
fication methods (e.g. logistic regression), or to probabilistic methods such as the one pro-
posed by Taddy (2015b). Alternatively, by selecting several known positive and negative
seed words, the vector space can be used to pinpoint words adjacent to those seed words
and consider them as carrying the same polarity. The SENTPROP method from Hamil-
ton et al. (2016) first constructs a lexical graph from a VSM with the words connected
according to their embedding using cosine similarity and then performs label propagation
to define the polarity. The sentiment score of a word is proportional to the probability
of a random walk hitting that word, as propagated starting from a seed set. To obtain
confidence bands around the scores, they bootstrap over random subsets of seed words.
In the same vein as for lexicons, learning algorithms are ideally adapted for specific do-
mains and languages to optimize the sentiment quantification. Thus, for optimal accuracy,
the analysis for a specific domain needs a separate annotated data set, as opposed to using
an annotated broad corpus and the resulting generic trained algorithm. Transfer learning
is the strand that investigates the optimal conversion of methods in one domain or one
language to another. Good transfer learning minimizes the burden on the researcher to
acquire equally informative domain-specific annotated corpora for all domains of interest.
An application of transfer learning is to deduce sentence-level sentiment from document-
level sentiment labels. T¨
ackstr¨
om and McDonald (2011) use hidden conditional random
fields as a latent variable structure model to deduce the latent sentence-level sentiment.
6.2. Audio and Visual Data
Some of the tools discussed for textual sentiment computation are also of value for the
extraction of sentiment from audio, and visual data. A lexicon can be constructed with
entries such as “light smile,”“big smile,”“eye contact,”“crying,”“shouting,”“high pitch,”
or “low pitch,” all with a certain calibrated polarity, and the number of seconds the action
is held as a measure of polarity strength.
Domain specificity can be thought of as speaker specificity in the context of audio
data. Speaker-dependent approaches give (much) better results than speaker-independent
approaches (Poria et al.,2016). The number of possible speakers is almost always larger
than the number of possible languages or domains, making it infeasible to develop a
specific algorithm for every individual speaker. However, making algorithms for types of
speakers (e.g. political speakers) makes sense and is achievable.
Rousseeuw et al. (2018) define a measure of directional outlyingness that is applied on
image data to detect (sudden) changes in how a video frame appears relative to another
frame. A transformed aggregation of the various outlyingness measures would make a
good candidate as a proxy for sentiment.
17
7. Aggregation of Sentiment Variables
Most researchers are not interested in an entity’s or a data unit’s sentiment at one
specific point in time but in the average value on several moments, or across many entities,
methods, and data sources. Therefore, appropriate aggregation is required.
7.1. Within-Unit
An essential aspect of the sentiment quantification as discussed in Section 6is within-
unit aggregation. For textual data, this becomes within-document or intratextual aggre-
gation. Within-document aggregation is the weighting of the document-level sentiment
information (e.g. the sentiment of a word or of a sentence) into a score that represents
sentiment for that document. For visual data, this becomes, for instance, within-video
aggregation, which consists of the aggregation of sentiment of the different segments of
the video into a whole video sentiment score.
A widely used weighting scheme, in preprocessing and for text aggregation, is the
tf-idf statistic. This scheme weighs terms based on their frequency of occurrence (“tf”),
but revalues upward the words appearing across few documents (“idf”), under the idea
that less frequent terms can be of greater value to detect the specificity of a document.
This weighting approach makes document specificity a function of term use rather than
term meaning. Another option is to weight based on reader’s attention, which could be
assumed higher in the beginning and end of a text. Allee and DeAngelis (2015) find
an important degree of dispersion of sentiment in financial disclosures. Documents have
typically one dominant sentiment class but no uniform sentiment across paragraphs or
sentences. Boudt and Thewissen (2019), for example, show a clearly U-shaped pattern of
sentiment within CEO letters.
Poria et al. (2016) outline two approaches to aggregating, or fusing, textual, audio,
and visual signals, which happens when dealing with video material. A first strategy is to
combine characteristics from every type of data into a joint vector and use this vector as
input in a classification algorithm. The second strategy is to model sentiment individually
per data stream, and then combine the unimodal results based on suitable metrics and
weighting. The dynamic weighting of the unimodal results is an interesting research issue
to explore. Pham et al. (2018) propose a third strategy, closest related to the first strategy,
aiming at a joint multimodal representation. They use an unsupervised encoder-decoder
framework but admit that a unimodal textual approach led to the best overall results in
their empirical video analysis.
7.2. Cross-Sectional
Cross-sectional aggregation can occur at multiple levels. A first level is across docu-
ments at a given frequency, which results in a time series. This across-document aggrega-
tion is the natural next step after within-document aggregation. For example, to obtain a
weekly time series, all sentiment scores need to be aggregated at a weekly frequency. An
interesting possibility for the aggregation is to let the weights depend on the articles’ reach
(e.g. the number of reads). One can then decide to further adjust the weights based on
some empirical knowledge—for example, to cope with the underrepresentation of far-right
voters on social media, as suggested in Ceron et al. (2014).
A second level is across documents for a given metadata marker. For instance, one
could aggregate sentiment scores for all documents coming from a given source, or dis-
cussing a certain entity. Only considering a limited number of sources to measure senti-
ment for a given period risks to give a biased estimate due to an unrepresentative sample.
18
Typically, the first and the second level are combined to obtain a time series for a given
metadata occurrence. Many of such combinations capture different dynamics of the corpus
and its metadata. Borovkova et al. (2017) obtain weekly sentiment values by a weighting
that takes into account the relevance and novelty scores supplied by the Thomson Reuters
News Analytics database.
A third possible level of cross-sectional aggregation is across sentiment methods. The
order of when to do this aggregation depends on the goal. In the simplest scenario, only
one method is used, or multiple methods are kept side by side—meaning no across-method
aggregation at all. Another simple scenario is to average the sentiment scores from any
given number of methods to obtain an averaged sentiment score. Boudt et al. (2018) take
the centered average of the scores coming from the lexicons they apply. A more statistical
approach is commonality extraction, using principal component analysis or latent factor
modeling. Rogers et al. (2011) define sentiment as the first principal component over a
range of sentiment measures. Last, an objective-based approach optimally weighs different
methods based on their relationship with a target variable or based on another quantifiable
objective. We further develop the techniques, problems, and open questions regarding the
last two approaches in Section 8.
7.3. Across-Time
Across-time aggregation aims to smooth obtained sentiment time series or, more gen-
erally, to infuse a certain time dependency pattern. There are various valid reasons for
smoothing. One of those is to remove outliers. This especially holds for short-term sen-
timent series, for example at a daily frequency. Thorsrud (2020) applies a 60-day moving
average to his daily tone-adjusted textual topic time series to filter out the noise. An-
other motivation for smoothing is related to the belief that sentiment at a certain time
usually also partly reflects earlier sentiment. Sentiment needs to be updated when new
information arrives but remains affected by previous information. Ardia et al. (2019b), for
example, use beta weighting schemes covering a large number of possible time dynamics.
They use a data-driven calibration to deal with the problem of not knowing in advance
which time pattern has the most value for forecasting. The Kalman filter is also an ap-
propriate technique to smooth out sentiment time series. It can be used to retrieve the
unobserved sentiment state from the observed (already aggregated) sentiment variable.
Borovkova et al. (2017) employ a simple local level state space model, leading to signifi-
cantly less noisy sentiment variables. Shapiro et al. (2018) use a monthly fixed effect as
time series sentiment indicator, controlling for newspaper and article type fixed effects.
7.4. Across Variables or Proxies
The combination of the likely heterogeneity in the input data, the number of variables
that can be associated to the data, and the number of sentiment implementations and ag-
gregations may give rise to many constructed sentiment time series. For instance, Gelper
and Croux (2010) use a one-factor model, estimated either as the first principal compo-
nent or using partial least squares, to form an aggregate sentiment indicator from 160
sentiment proxies. In Ardia et al. (2019b), the different sentiment variables are weighted
and assembled into a sentiment-based index using the elastic net regression. The obtained
sentiment index is specific to the dependent variable used in the regression. Aggregation
here is thus across metadata as well, which is usually not done at the across-document
level. For example, to measure the sentiment around the economy, one may want to obtain
this sentiment as a weighted average of several components such as employment, produc-
tion, and the business cycle. Borovkova et al. (2017) obtain a final aggregated weekly
19
sentiment index as an average of sentiment indices about important financial institutions,
weighted by a bank-related measure such as net debt.
In a multivariate setting, one can repeat this process of creating separate sentiment
indices for a series of proxies and then aggregate across these sentiment time series to
obtain a final sentiment measure. That measure ought to be the optimized representation
of the latent variable that is assumed to be represented by the collection of proxies. An
example of a latent variable is the reputation of a company, which depends on observable
variables such as profitability, market share, stock returns, and sustainability. Simplicity
in weighting might be desired (e.g. equal weighting), but more complex (aggregation)
schemes deserve to be studied. Larsen and Thorsrud (2019) use the marginal likelihoods
across predictive regression models to form weights aggregating text-based time series into
an index that best captures the variable to predict. Going forward, the idea of forecast
combination could be useful for across-proxy aggregation.
Nimark and Pitschner (2019) define two interesting aggregated measures based on topic
probabilities coming from a probabilistic topic model. The first is topic-specific deviation
of a certain news topic (“specialization”); the second measures the news homogeneity in
terms of agreement which topic is deemed most important. Empirically, they use the
measures to show that different news sources emphasize different topics, but major events
make news coverage more homogeneous. Similar measures could be constructed to test
for the sentiment agreement across various sources.
Creating interactions of sentiment time series with other variables allows testing their
interplay in explaining a dependent variable. The joint assessment of sentiment and
topics is most prevalent in the literature (see e.g. the sentiment-adjusted topic measures of
Thorsrud,2020, or the context-specific sentiment time series in Calomiris and Mamaysky,
2019). Calomiris and Mamaysky (2019) and Glasserman and Mamaysky (2019) use an
entropy-based measure to characterize a collection of news during a given time frame
in terms of “unusualness” and create simple interaction terms with sentiment variables
aggregated at the same frequency. These interaction terms add information, allowing
one, for example, to uncover that negative unusual news leads to an increase in U.S.
stock market volatility (Glasserman and Mamaysky,2019). Boudt et al. (2018) assess the
interaction of sentiment with various company variables (finding that the informativeness
of sentiment depends on the level of information asymmetry), while Arslan-Ayaydin et al.
(2016) interact sentiment with managerial compensation (finding that the informativeness
of sentiment depends on the incentives to manipulate the sentiment). Garc´ıa (2013)
interacts a measure based on the New York Times news with a dummy variable to indicate
a recession and concludes that daily stock returns are better predicted during recessions.
8. Modeling
This section is mainly approached as the problem of modeling an outcome variable Y
as a function of the sentiment variables stored in a matrix S, and possibly a number of
control variables in another matrix X. It can very generally be seen as modeling the joint
density function f(Y, S,X).
8.1. Time Series Models
A very simple setup exists in modeling the output variable with a small number of
sentiment variables and possibly other explanatory variables through a linear regression.
Simple means it can be solved with ordinary least squares (OLS) regression. Penalized, or
regularized, regression is required when OLS regression cannot be applied—that is, when
20
the number of explanatory variables is too high relative to the sample size, or when there
is a severe problem of multicollinearity. Regularization of a high-dimensional variables set
shrinks the coefficients of the least informative variables toward zero. The Ridge (Hoerl
and Kennard,1970) and the LASSO (Tibshirani,1996) approaches are the most common
ways to specify the penalized regression. The elastic net regularization of Zou and Hastie
(2005) embeds both the Ridge and the LASSO.
Factor models extract one or more latent common patterns among a set of time series.
Thorsrud (2020) develops a mixed-frequency time-varying dynamic factor model from
which he extracts a daily news-based coincident index of business cycles. Both the mixed-
frequency and (dynamic) factor aspects are useful approaches. For the first, for example,
sentiment aggregated at both weekly and quarterly frequency could be fed through a
mixed-frequency factor model to obtain a short-term, a long-term and an overall trend.
Similarly, grouped data settings can be used to extract common sentiment in groups of
time series—for example, a common factor for every industry group consisting of all firms’
sentiment measures. Andreou et al. (2019) derive asymptotics to identify common and
group-specific factors in such a setting. Specifically, they introduce a test to assess which
factors are common across a set of group-specific vectors.
The news-based measure from Manela and Moreira (2017) is an estimate from an SVM
regression using the VIX index as dependent variable and normalized n-gram counts
from texts as independent variables. This is a valid way to create a final optimized
index—that is, to let an index be constructed from how well it captures a target variable.
However, using such sentiment proxies in a second-stage regression usually has an impact
on the uncertainty surrounding the then estimated coefficients. Manela and Moreira
(2017) adjust the standard errors around the eventual point estimates to account for the
uncertainty that is introduced by the first-stage regression.
Many target variables of interest could be discrete—for instance, an indicator variable
whether a month lies in a recession period or not. Regularization is also perfectly ap-
plicable in a nonlinear context. Pure machine learning algorithms, such as SVM, neural
networks, or Random Forest, are more relevant in a nonlinear setup, also applicable in
case of time series variables.
Multiple sentiment variables and target variables can be jointly modeled in a multi-
variate regression framework, such as vector autoregression (VAR) models (see Qin,2011
for a historical development of VAR models, and L¨
utkepohl,2017 for a survey on struc-
tural VAR models). These frameworks are in general less prone to identification issues,
since the variables are treated as endogenous, unless when explicitly considered exogenous
or not modeled.
8.2. Generative Models
One can distinguish between two key econometric approaches to measuring sentiment
(Gentzkow et al.,2019a). Sentiment is either seen as a function of the written text
(sentiment = f(text)), or the written text is seen as a function of the underlying sentiment
(text = f(sentiment)). In the latter case, sentiment can be considered as a parameter of a
stochastic process that generates texts as realizations. A seminal research paper in this is
field is by Blei et al. (2003) proposing the latent Dirichlet allocation (LDA) model. Under
this model, documents are assumed to be random mixtures over a predefined number
of latent topics, where each topic is characterized by a distribution over words. Fitting
such a model on a corpus of texts allows studying topic prevalence (the proportion of a
document devoted to a topic) and topic content (the words used to discuss a topic).
21
Blei and Lafferty (2006) come up with a dynamic topic model that allows the content of
the topics to change over time. Blei and Lafferty (2007) extend the LDA model by making
correlation across topic proportions possible. Roberts et al. (2016) develop a structural
topic model that lets the discovery of topics be a function of both word counts and
observable covariates. These covariates can consist of sentiment variables, or metadata
such as author and time of publication. The generative paradigm in a sentiment context
thus starts from a statistical model that should be viewed as the source of all statements
generated. For example, a model can be set up in which tokens are hypothesized to follow
a generative model conditioned on a sentiment variable.
Taddy (2013b) introduces a framework to obtain low-dimensional document represen-
tations rich in sentiment information, called multinomial inverse regression (MNIR). He
defines sentiment as the observable variables (e.g. product rating or whether a text is pos-
itive or not) impacting the composition of text data. Hence, his approach clearly follows
the “text = f(sentiment)” assumption. The most probable sentiment output can be asso-
ciated with any unseen text using forward regression. Taddy (2015a) extends the MNIR
framework to also account for potentially larger dimensions of the sentiment variables,
referred to as distributed multinomial regression (DMR).
8.3. Combining Time Series Models and Joint Generative Models
Given the natural role that topics play as metadata features, the joint generative
modeling of topics and sentiment is very useful, especially when a time series perspective
is included. The dynamic topic model framework of Blei and Lafferty (2006) can be
deemed a time series generalization of the topic models proposed earlier. Eguchi and
Lavrenko (2006) address both the topic and sentiment of a text unit using probabilistic
generative modeling. Every statement is considered to have a set of topic-bearing and a
set of sentiment-bearing words, each coming from respectively an underlying topic and
sentiment language model. The dependence between both models is explicitly taken into
account, under the assumption that sentiment depends on the topic. This assumption is,
for example, supported by the importance of domain-specific sentiment lexicons.
Lin and He (2009) jointly extract document-level sentiment and the mixture of topics
using an unsupervised procedure. They go from the three-layered LDA (topics associated
with documents, and words associated with topics) to their joint sentiment/topic (JST)
model, having four layers (sentiment labels associated to documents, topics associated
with sentiment labels, and words associated with sentiment labels and topics). The joint
sentiment and topic modeling answers to the need for domain specificity of sentiment
analysis. It generally is approached as a two-stage process: first the detection of topics,
then the assignment of sentiment labels.
He et al. (2013) and Fu et al. (2015) further develop two related joint sentiment-
topic models that allow selected dynamic parameters to account for the time-variation in
topics and sentiment. The inclusion of external variables makes it easier to interpret the
driving processes behind discourse and content of qualitative material. In the approach of
Gentzkow et al. (2019b) to measure trends in the degree of polarization in political speech,
one can, for instance, include observed and unobserved speaker-specific characteristics.
There does not seem to be any longitudinal approach that uses the current state
of a set of external variables (e.g. representing the economic and financial markets) as
drivers for the time variation of the used sentiment and topics in written media articles.
Such a holistic parametric model has, however, clear advantages in terms of econometric
inference about the relationship between the observed news coverage, the features of the
news sources, and the time variation in the variables system.
22
8.4. Normal and Abnormal Sentiment
There are several modeling approaches to decomposing sentiment into a normal and
an abnormal component. Huang et al. (2014) distinguish between normal tone and ab-
normal tone, defining abnormal tone as the residual of a regression of tone on firm-specific
characteristics. Ardia et al. (2019a) make the same distinction. They similarly consider a
regression approach but use a static observable factor model, more precisely a market-cap
weighted sentiment index, with abnormal tone also the residual. Other alternatives could
be to use the residuals of a simple mean model or of a latent factor model.
Hubert and Labondance (2018) identify sentiment as the unpredictable component of
lexicon-based textual tone, orthogonal to a series of variables representing economic fun-
damentals. In other words, they define sentiment as the soft information conveyed through
the tone of a communication beyond traditional quantitative and qualitative information
conveyed through the content. Sentiment is obtained as the residual, with its first-order
autoregressive component removed, from a regression on the variables representing the
fundamental content.
8.5. Attribution Analysis for Model Interpretation
Interpretation is strongly tied to the problem definition and generally qualitative. On
the statistical side, we point out attribution analysis to interpret measured, nowcasted,
and forecasted sentiment.
Sentiment aggregation and modeling condenses a lot of information into a few quanti-
tative sentiment representations of interest. A natural question is then how much of the
final value is explained by the input data. Obtaining such a decomposition of the final
value into the contributions of the component input data is the purpose of a top-down
attribution analysis. These constituents are weighted based on their relationship with a
target variable and thus allows studying the relative importance of every constituent or
of groups of constituents. This in fact is a more fine-grained approach to doing sentiment
decomposition, though typically not model based. Aggregation based on the metadata
features allows obtaining a predefined decomposition of the relevant sentiment and may
help with identifying the underlying sentiment drivers in relation to a target variable.
Because of the linearity of the aggregation performed in Ardia et al. (2019b), the attri-
bution to any of the aggregation dimensions could be easily obtained. For example, they
attribute the full sentiment-based forecast of the U.S. industrial production growth to six
clusters of separate economic topics. The aggregate news index from Thorsrud (2020)
can also be decomposed in terms of topic contribution. An interesting avenue to explore
is to do the same attribution to various news sources and bring this into relation to how
readers are exposed to these sources and their potential media biases. Larsen et al. (2020)
analyze the variation in attribution by looking at the proportion of attribution that is
unchanged for model updates up to 60 months in the future. During the global financial
crisis, the predictive attribution relationship turned out to be much less stable, with only
a small proportion of the explanatory news variables remaining important. This speaks
in favor of doing regular model reestimations when times are troubling to incorporate the
relevant news. Calomiris and Mamaysky (2019) also detect strongly time-varying coeffi-
cient estimates for news measures when forecasting the stock market. This is due to both
the changing mix of the news sources as well as the actual impact of the news. Interest-
ingly, Larsen and Thorsrud (2018) find that narratives mostly go viral during downs in
the business cycle, albeit for a duration of only a few months.
23
In case of multivariate economic systems, impulse response functions in the vector
autoregression (VAR) framework are usually used for interpretation. An impulse response
function describes a variable’s evolution along a specified time horizon after a shock in the
regression system. When a meaningful sentiment shock is infused, its impact on all other
variables can be quantified and understood across time. Borovkova et al. (2017) analyze
the impact of a one standard deviation change in sentiment on various macroeconomic
variables and find it to last significantly up to two months later.
9. Validation
The entire workflow is about extracting sentiment variables from qualitative data
and using those variables in an economic analysis. Validation takes place at the end of
every step but can be broken down into four categories: (1) evaluation of the quality
and selection of the data, (2) evaluation of the sentiment quantification and aggregation,
(3) model estimation and hypothesis testing, and (4) evaluation of the out-of-sample
statistical and economic performance of the model-based predictions.
Many choices in the econometric analysis of textual, audio, and visual sentiment re-
main ad hoc. To adequately gauge the presence and impact of sentiment, the entire
analysis should be frequently validated in a problem-specific way, both quantitatively and
qualitatively. Comprehensive validation combines tools from econometrics with tools from
machine learning. Machine learning is mostly about accuracy of prediction; econometrics
is about uncovering (causal) relationships between economic variables.7Validation essen-
tially jointly tests the current step and all previous steps as to whether they satisfy the
assumptions for correct further (econometric) analysis.
When a sentiment variable does not seem to have a significant effect on the variable
of interest, it may be due to two things. Either there is no significant effect of sentiment,
or there is a significant effect, but the sentiment variables used are a weak proxy for
real sentiment and do not capture the significant relationship. This can be conceived as
a “joint hypothesis” problem. In order to mitigate this problem, the validation in the
field of sentometrics is largely twofold. First, one should validate the sentiment variables
created and then the model. When a model is deemed adequate in a statistical sense,
further validation includes the interpretation of the results. A sentiment-based model that
cannot be interpreted is not useful to convincingly answer the question outlined.
9.1. Data Quality and Data Selection
Since textual, audio, and visual data arrive in raw formats, the quality can vary
substantially. Chances are not all data units are fully cleaned even after preprocessing.
Data quality checking is an iterative process. It is natural to go back to the cleaning and
selection when some errors are found a few steps further in the workflow.
A basic quality check asks whether everything necessary for analysis is present. For
instance, to be able to do a time series analysis, time stamps are inevitable. Any prepro-
cessing of data involve a clear trade-off between simplifying the data and information loss.
Denny and Spirling (2018) document the sensitivity of textual preprocessing choices on
7Advancements in machine learning and econometrics have been going more hand in hand. An inter-
esting example is “double” or “orthogonal” machine learning, a development that aims to deal with the
invalidity of inference infused by many machine learning methods (see mainly Chernozhukov et al.,2017
and related work).
24
the outcome of an unsupervised analysis. They devise a scoring and regression approach
to quantify this sensitivity.
Validation of the data quality and its selection exists in minimizing the exposure to
the limitations described in Section 4.3 or acknowledging them going forward. Ideally, the
selected data are maximally spread out across relevant data sources. If there are several
major broadcasters but data for only one is available, there is a severe risk of bias when
generalizing any obtained results from this restricted data set, as opposed to being only
interested in and sticking with the conclusions of the particular data source studied.
Directing the analysis of audio data via speech-to-text to a textual analysis brings
up the question of how trustworthy the conversion was. It is important to treat every
transformation step and its possible errors as such, not confusing the textual data for the
actual source audio data.
The data should be controlled for duplicates or near duplicates. If the duplicated data
entries come from a different source, the content has likely been consumed more widely.
A way to omit duplication but still maintain the implications it has is to add a metadata
component that counts the number of duplicated occurrences. Wang et al. (2014) provide
a (technical) overview with different techniques useful for duplicate detection.
9.2. Sentiment Quantification and Aggregation
The quantification of sentiment is highly important because it provides the numbers
that any further step and interpretation is based on.
Relying on machine learning to train sentiment classifiers works under the assumption
that the annotated data set is a faithful representation of the actual sentiment. Not every
annotation procedure leads to a reliable annotation set. The quality of the gold standard
can be measured by the level of inter-annotator agreement using, for instance, Cohen’s
kappa. To measure the effectiveness of a sentiment classifier or a lexicon, one has to
compare the model-generated scores with the gold standard. More precisely, the trade-off
between precision (the proportion of positives that is correct) and recall (the proportion
of positives that is found) is at stake.8Recall and precision extend easily from a two-class
problem (e.g. positive sentiment versus negative sentiment) to a multiclass setting doing
micro or macro averaging (see e.g. Zhang and Zhou,2014).
Every lexicon tends to undergo one or more rounds of expert-based checks, to explic-
itly classify words into positive or negative, delete irrelevant words, and correct obvious
mistakes. The validity of individual entries of lexicons are thus still mainly evaluated by
humans. Overall, lexicons should undergo the same level of scrutiny as any other senti-
ment computation method in terms of validation. It should be tested if the accuracy of
domain-specific lexicons is higher than generic lexicons. Loughran and McDonald (2011)
use careful inspection of frequently occurring words as the only basis to create their al-
ternative word lists. To validate this procedure, they relate tone computed from their
negative lexicon to filing period excess stock returns, finding this sentiment measure to
be in general more significant than tone based on the generic Harvard dictionary negative
lexicon. The approach of Labille et al. (2017) compares a set domain lexicons on other
domain texts. If the domain-specific lexicon is well constructed, it should rank first in
terms of accuracy for the domain it is designed for. Apart from accuracy levels, another
8The precision and recall metrics can be combined in the Fβ-score, with Fβ(1+β2)precision×recall
β2
×precision+recall .
The βfactor defines the relative level of importance put on recall. If β= 1, both metrics are weighted
equally in a harmonic mean sense.
25
simple comparison procedure is an ANOVA analysis to see which lexicon’s score variabil-
ity is best captured by human coders. When the lexicon is generated with a regression,
one looks at fit or information criteria statistics to validate the overall power of a lexicon
(e.g. Pr¨
ollochs et al.,2015). An imbalance between positive and negative entries might
make sense from a domain-specific perspective but should be defendable, since bias in the
sentiment quantification algorithm can also be due to a biased training set. The Loughran
and McDonald dictionary, for instance, is left with the large proportion of 78% negative
words as a result of the domain adaptation to financial disclosures.
When creating sentiment measures, a first and simple analysis is to determine the cor-
relation with existing related sentiment time series. All EPU indices of Baker et al. (2016)
were validated using a very diligent human audit process, showing that the computer-
generated indices are highly correlated with the human-generated ones. Soo’s (2018) me-
dia sentiment housing index correlates strongly with the University of Michigan Survey
of Consumers, albeit lagging. He further validates his index by confirming a reasonably
strong lagged correlation with a multifactor index that combines multiple proxies, con-
structed based on the methodology of Baker and Wurgler (2006). The most difficult task
can end up to find related proxies, as sometimes they are rare or do not exist at all.
Another simple time series validation procedure is what is referred to as event validation.
This entails visualizing a sentiment measure and confirming whether sharp increases or
drops coincide with the incidence of important events that intuitively would result in a
strong increase or decrease in sentiment, respectively.
9.3. Econometric Modeling and Interpretation
Many models are evaluated by measuring the accuracy in an out-of-sample prediction
exercise. However, prediction is not always of interest; measuring which words and how
they convey sentiment can be a more important objective that is not always related to
prediction accuracy. As mentioned in Justin Grimmer’s comment on Taddy (2013b), how
to do trustworthy task-specific sentiment evaluation still needs to be formalized. How
is one to know with a high degree of confidence whether a token can be attributed to a
particular sentiment feature? This problem can be particularly apparent when doing a
large-dimensional regression of a sentiment variable on unigrams, for instance, with the
resulting coefficients of the unigrams not always easy to interpret and sensitive to change
across different specifications.
The problem of extensive and problem-specific validation is brought up in detail in
Grimmer and Stewart (2013). For supervised methods, validation is fairly straightfor-
ward; it boils down to minimizing the prediction error in replicating a set of annotated
outputs or maximizing the classification accuracy (typically making use of confusion ma-
trices). A data set is best divided into a training, a validation, and a testing set to avoid a
biased view on accuracy due to overfitting (Varian,2014). Alternatively, one can do k-fold
cross-validation or rolling forecasting origin cross-validation when dealing with time se-
ries. Unsupervised methods require combining experimental, substantive, and statistical
evidence to show the conceptual validity of a model output. Proper validation of unsu-
pervised models is especially important when used for inference or measurement rather
than prediction or exploration (Roberts et al.,2016).
9.3.1. Model Estimation and Hypothesis Testing
It is common to evaluate the in-sample goodness of fit of a sentiment-based regression
model with the (adjusted) R2statistic. When adding their word flow measures, Calomiris
26
and Mamaysky (2019) find a substantial increase in the R2for predicting returns, volatil-
ity, and drawdown risk. The main concerned parameters are those associated with the
sentiment variables. Their significance should be assessed statistically and economically.
Statistical significance shows whether an effect exists, but its applicability is mainly lim-
ited to low-dimensional models. Gandomi and Haider (2015) review various issues of
doing econometrics in a big data environment, pointing out the “irrelevance of statisti-
cal significance.” Economic significance inspects the sign and strength of the association.
Economic meaning can be given through, for instance, an attribution analysis.
In general, textual, audio, and visual data bring the known endogeneity challenges to
econometricians. The creation and publication of texts, videos, and speeches is correlated
with many factors, so positing a cause and effect remains dangerous when no further
insights into the (many) underlying factors of the data are available. Is it the sentiment
of the alternative data set that is at the heart of a certain correlation or causality, or is
the sentiment a reflection of associated underlying factors? Does the sentiment impact
the outcome variable directly or indirectly, and through what mechanism? Larsen and
Thorsrud (2018) partition their network of sentiment/topic variables into more and less
exogenous variables. Variables are considered exogenous if they have predictive power
for other topics but are not (often) predicted themselves. The most exogenous variables
seem to be associated with economic fundamentals. Hubert and Labondance (2018) cor-
rect for endogeneity in their central bank tone measure by stripping away fundamentals,
expectations of future fundamentals, standard monetary shocks, investor sentiment, and
past sentiment shocks. Benhabib and Spiegel (2019) deal with endogeneity and, more
specifically, reverse causality using instrumental variables. They use political data to
instrument for differences in (survey-based) sentiment levels by state. When testing the
effect of sentiment on the target variable and finding significant results, it is recommended
to also test the effect of the target variable on sentiment via a reverse (lagged) regression
specification. Few research papers on sentiment have carried forward this robustness step.
Model uncertainty is assessed through analyzing the impact of sentiment parameter
estimates across various model specifications. This has to do with both a good and
exhaustive definition of the control variables Xand with testing for enough different model
structures. Soo (2018) creates robustness variables from the qualitative data themselves.
He computes indices from those news articles that convey fundamental market information
rather than sentiment, adds those to his regression specifications, and finds that his major
sentiment index remains significant. Varian (2014) states it is important “to be explicit
about examining how parameter estimates vary with respect to choices of control variables
and instruments.” Validation is rarely a black-and-white matter. The researcher should
identify when and how sentiment is informative and when it is not.
9.3.2. Out-of-Sample Evaluation
An out-of-sample version of the R2statistic can be used to measure the relative re-
duction or increase in the mean square out-of-sample prediction error of a sentiment-
based forecasting strategy with respect to a baseline strategy. Using the out-of-sample
R2,Ad¨
ammer and Sch¨
ussler (2020) document statistically significant increased predictive
power of the monthly U.S. equity premium when using news-aggregated variables com-
bined with a model-switching strategy. Caporin and Poli (2017) use five metrics (mean
absolute error, mean square error, heteroskedasticity adjusted mean square error, QLIKE
loss function, and R2of Mincer-Zarnowitz forecasting regressions) to compare the fore-
casting performance of a news-based realized volatility model versus a baseline.
27
The magnitude of the impact of sentiment variables on economic and financial vari-
ables is highly subject to time variation. Stability needs to be tested by performing
the analysis, and measuring the performance, on various subsamples, or by doing rolling
forward regressions.
A simple way to sidestep the issue of endogeneity is by comparing existing linear models
to models enhanced with the quantified alternative data sources and to simply focus on
whether predictive power improves or existing (significant) relationships hold. This could
be formulated as testing models “controlling for sentiment.” The model confidence set
procedure from Hansen et al. (2011) allows testing whether different model specifications
are truly different according to some significance level.
10. Software
This section points to a selection of useful software tools to carry out a detailed sento-
metrics analysis from textual data.9The selection is by no means exhaustive—meaning,
there exist plenty of other software tools equally of use to perform (parts of) a sentometrics
analysis. We limit ourselves to the open-source Rand Python programming environments,
due to their large popularity, strong communities of developers, and relatively gradual
learning curves. For instance, MATLAB rarely comes to mind for doing textual analysis,
but its Text Analytics Toolbox has many capabilities for doing powerful preprocessing,
vectorization, sentiment analysis, and topic modeling. One does not necessarily have to
choose one programming environment. Like Glasserman and Mamaysky (2019), a com-
mon workflow includes doing the handling of textual, audio, and visual data in Python,
and the statistical analysis in R. The available software is linked to specific tasks involved
in an econometric analysis of qualitative sentiment data and is summarized in Table 1.
The quanteda package (Benoit et al.,2018) is a general text mining toolkit in R.
Its development has been actively supported by the European Commission. The package
tidytext (Silge and Robinson,2016) can also be used to do many text processing tasks,
following “tidy” data principles. The tm package (Feinerer et al.,2008) is an older textual
analysis framework, but is still used as a backend in many text-related Rpackages.10
The NLTK library (Bird et al.,2009), short for Natural Language Toolkit, is the
text mining toolkit counterpart in Python, albeit even more exhaustive.11 In Python, the
spaCy library (Honnibal and Montani,2017) is the most complete alternative. It is faster,
but more black box. The TextBlob library (Loria,2019) is built on the NLTK library
and is therefore more specialized as to what concerns several textual extractions, such as
sentiment analysis through machine learning classification.
9A well-known open-source software tool for audio data processing is openSMILE (Eyben et al.,
2013). The LVA software (https://lva650.com) can be used for preprocessing, deconstruction, and
immediate emotion analysis of audio data (see Mayew and Venkatachalam,2012 for an application in
finance). For visual data processing, alternatives are the commercial softwares OKAO Vision System
from OMRON (https://plus-sensing.omron.com/technology) or Luxand FaceSDK (https://www.
luxand.com/facesdk), both mainly for facial features extraction. A good commercial speech-to-text
technology is Vocapia (https://www.vocapia.com). In the open source sphere, the DeepSpeech project
(Hannun et al.,2014) and associated software packages are very useful. Generally, the outputs returned
by the above tools can be easily loaded into any programming environment to perform the remaining
steps in the analysis.
10A helpful starting point to explore the plethora of textual analysis tools in Ris CRAN’s Task View
“NaturalLanguageProcessing” (https://CRAN.R-project.org/view=NaturalLanguageProcessing).
11The quanteda package website gives an overview of the actual functions across the packages referred
to perform several specific tasks (see https://quanteda.io/articles/pkgdown/comparison.html).
28
The Rpackage sentometrics (Ardia et al.,2020) provides a collection of functions
to do sentiment computation, sentiment aggregation, and (high-dimensional) sentiment-
based regression. Wischnewsky et al. (2019) use the package to create a “Sentoindex”
that represents financial stability sentiment as expressed during testimonies at U.S. Con-
gressional hearings. The sentiment computation in sentometrics is lexicon based, but
other sentiment scores can be used as input for further aggregation. The sentometrics
package also provides a simple keywords-based approach to generating metadata features.
The SentimentAnalysis package (Feuerriegel and Pr¨
ollochs,2019) can be used to create
lexicons and compute sentiment according to the method of Pr¨
ollochs et al. (2015).
The regression framework in sentometrics relies on both the caret (Kuhn,2018)
and glmnet (Friedman et al.,2010) packages but is specific to the sentiment time series
generated within the package. The glmnet package implements various penalized re-
gressions; the caret package provides more generic classification and regression modeling.
The inverse text regression methods developed by Taddy (2013b) and Taddy (2015a) are
available in the Rpackage textir (Taddy,2018).12 The rJST package (Boiten,2019)
implements the joint sentiment/topic model of Lin and He (2009).
Python’s scikit-learn (Pedregosa et al.,2011) is one if its most established machine
learning libraries. It supports the majority of the common learning algorithms used in
sentiment analysis and is easy to use with respect to feature engineering. To do the same,
but also particularly deep learning, Google’s TensorFlow library (Abadi et al.,2016) is
the standard, albeit imposing more on the user in terms of setting up the individual com-
ponents of a chosen model. Since recently, there also exists a comprehensive Rinterface
to the TensorFlow framework.
These days, research papers also go increasingly accompanied with standalone open-
source replication code (see e.g. the MATLAB code used in Thorsrud,2020).13 Another
example, to do sentiment analysis benchmarking, is the online tool iFeel 2.0 (Ara´ujo et al.,
2016) based on Ribeiro et al. (2016).
A shortcoming of the current software landscape is that there are no libraries that
propose a full and easy integration of the required data handling, machine learning, and
econometric tools. The preprocessing and sentiment quantification packages have very
little in common with the packages used for modeling. Having to combine too many
packages or even multiple programming languages is prone to error, for instance, due to
the usage of different types of object classes that need to be converted.
12The DMR from Taddy (2015a) is also implemented with the programming language Julia, avail-
able at https://github.com/AsafManela/HurdleDMR.jl, which mainly includes the Hurdle Distributed
Multiple Regression algorithm from Kelly et al. (2019).
13The code is available at https://github.com/leifandersthorsrud/NCI.
29
Table 1: Nonexhaustive overview of textual data analysis tools in Rand Python. The abbreviation ML stands for machine learning. A tick
indicates that the software can be directly or indirectly (i.e. by minimally chaining with other available tools) used to perform a particular workflow
step. The packages included for Rare caret (Kuhn,2018), glmnet (Friedman et al.,2010), quanteda (Benoit et al.,2018), rJST (Boiten,2019),
SentimentAnalysis (Feuerriegel and Pr¨
ollochs,2019), sentometrics (Ardia et al.,2020), textir (Taddy,2018), tidytext (Silge and Robinson,
2016), and tm (Feinerer et al.,2008). For Python, the libraries tabulated are NLTK (Bird et al.,2009), scikit-learn (Pedregosa et al.,2011),
spaCy (Honnibal and Montani,2017), TensorFlow (Abadi et al.,2016), and TextBlob (Loria,2019).
Tasks Restructuring Sentiment quantification Time series Econometric analysis
Software Cleaning Metadata Tokens Lexicon-based ML Aggregation Visualization Regression Validation
R
caret X X X
glmnet X X X
quanteda X X X X X
rJST X X
SentimentAnalysis X X
sentometrics X X X X X X
textir X X X
tidytext X X X X
tm X X X X
Python
NLTK X X X X X X
scikit-learn X X X X X X
spaCy X X X
TensorFlow X X X
TextBlob X X X X
30
11. Concluding Remarks
Sentiment analysis allows us to accurately and automatically map alternative data into
quantitative statistics as a support for decision making across many business applications.
Economists and investors, and also politicians and journalists, have started to embrace
the utilization of econometric methods in the analysis and application of textual, audio,
and visual data, to understand historical evolutions and better forecast future evolutions.
We overview the emerging field of sentometrics that investigates the transformation of
qualitative data into quantitative sentiment variables, and their subsequent application in
an econometric analysis of the relationships between sentiment and other variables. This
survey is organized around the different steps of a typical analysis. The most important
terminology is collected in Appendix A.
Textual, audio, and visual data will continue to become more cheaply and widely avail-
able, together with becoming more easily accessible. The interest of public and private
institutions to monetize these data and their proprietary data will grow as well. We rec-
ommend further research on multimodal sentiment analysis in econometrics. The future
will be exceedingly multimedia in terms of content generated, hence the analysis indis-
pensably multimodal. A major challenge is the development of appropriate technology
for unified multimodal sentiment analysis systems.
Progress toward better integrated and more reproducible sentiment data research will
require collaborative cross-disciplinary efforts. We end this paper with a call for more
efforts toward reproducibility in the econometric study of sentiment from qualitative data.
It would benefit greatly from reference data and associated state-of-the-art performance,
for different sentiment quantification techniques, data, and econometric approaches. In
the field of computer science, such practices are more widespread. Other researchers can
evaluate any new approach on the reference data and as such provide a consistent picture
of reproducibility or improved performance. Even though the sharing of code and data
has gained adoption, there are yet no standard practices on how to do so. The reference
data and results should be made available through an open database with easy access and
well-documented formats. This matches with the proposition of Lacy et al. (2015) to set
up a standard scholarly repository to share research-related materials. As a companion
to this survey paper, we have therefore set up a collaborative econometrics and sentiment
GitHub project to gather such resources.14
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Appendix A. Glossary
Corpus A corpus in linguistics jargon designates the collection of textual data units
(e.g. documents) to be analyzed. It can be generalized to indicate the collection of data
units from textual, audio, or visual data.
Features A feature is a broad term to represent any type of metadata attached to
the original textual, audio, or visual data as stored in a corpus. Examples are source,
expresser, entity, location, topic, and so on. This definition is slightly different but in
line with how features are used in a machine learning context, where they refer to the
set of explanatory variables. In video and audio data, (low-level) features are compact,
mathematical representations of the physical properties of the data (Wang et al.,2003).
Lexicon A lexicon is a list of tokens (e.g. words, a sequence of words, a facial ex-
pression, or a sound) with, for each token, an associated score that represents its average
38
sentiment. Also interchangeably called a sentiment lexicon, a sentiment word list, or a
sentiment dictionary.
Natural language processing (NLP) The broad subfield within artificial intelli-
gence occupied with the understanding, interpretation, and manipulation of human lan-
guage. It draws from computer science, computational linguistics, and machine learning.
Polarity The polarity (or semantic orientation) of an expression (whether it is a text,
a sound, or something else) represents its degree of positivity. Polarity categories go from
very positive to very negative, discrete or continuous.
Sentiment Sentiment equals the disposition of an entity toward an entity, expressed
via a certain medium. This working definition consists of (1) the expression by an entity
of its disposition, in the form of verbal or non-verbal communication, (2) the expression
has a polarity or a semantic orientation measurable on a discrete or a continuous scale,
and (3) the expression is oriented toward (an aspect of) an entity.
Sentiment analysis Sentiment analysis is about the extraction of sentiment from
the medium it is expressed through. Multimodal sentiment analysis covers textual, audio,
and visual media.
Sentometrics The term “sentometrics” is a portmanteau of sentiment and economet-
rics. It deals with the computation of sentiment from any type of qualitative data, the
evolution of sentiment, and the application of sentiment in an economic analysis using
econometric methods.
Supervised learning Supervised learning is a branch of machine learning that re-
quires an annotated data set (i.e. a set of input data with associated output values) to
train a model.
Unsupervised learning Unsupervised learning is a branch of machine learning where
the input data decide the output categories or representation by themselves. Any unsu-
pervised method is typically hybrid or semi-supervised, as there is often need for certain
minimal inputs from the modeler.
39
... A sentiment lexicon is a set containing words or phrases in a given language that are evaluated as being associated with a sentiment. The choice and evaluation of the lexicon are always controversial (for a discussion, see Algaba et al., 2019). From the various sentiment lexicons available for the Russian language (for a review and a methodological proposition for creating a unified lexicon see Kotelnikov et al., 2018), we have decided to use RuSentiLex by Loukachevitch and Levchik (2016), available at https://www.labinform.ru/pub/rusentilex/, ...
Article
The paper proposes a method of constructing text-based country-specific measures for economic policy uncertainty. To avoid problems of translation and human validation costs, we apply natural language processing and sentiment analysis to construct such measures for Russia. We compare our measure with that developed earlier using direct translations from English and human validation. In this comparison, our measure does equally well at evaluating the uncertainty related to key events that affected Russia between 1994 and 2018 and performs better at detecting the effects of uncertainty in Russia’s industrial production.
... An NLP system that is able to extract factual alongside subjective information is an invaluable resource for organizations and individuals: in marketing commercial products and services (De Clercq et al., 2017b;Pang & Lee, 2008), supporting non-profit organisations (Desmet & Hoste, 2013;Mostafazadeh Davani et al., 2019;, recommending products (Hsu et al., 2017;Y. Zhang et al., 2014), and -as in our case -in the economic and financial domain (Algaba, Ardia, et al., 2020;Gentzkow et al., 2019;Kearney & Liu, 2014). This latter domain is highly interesting since financial markets are largely driven by news that refers to macroeconomic factors, geopolitics, or companyspecific topics. ...
Thesis
Full-text available
To capture the vast knowledge expressed in written language, the field of Information Extraction within Natural Language Processing aims to obtain structured information on facts and opinions from unstructured text. Event extraction, on the one hand, is the task of automatically collecting the factual `who, what, where, when, why and how' of recent occurrences in news or social media. The processing of subjective opinions, on the other hand, is performed with sentiment analysis systems, where positive or negative attitudes are detected towards products, persons, or organizations. In this dissertation, we present the construction of an extensive dataset for fine-grained event extraction and sentiment analysis in economic news, named SENTiVENT. Subsequently, we validated our novel resource with machine learning experiments in which we apply state-of-the-art deep learning models to check the feasibility of our task. We defined economic events as prototypical schemata in which words expressing an event of a certain type (e.g., product releases, revenue increases, security value movements, deals) are linked to the participating persons, companies, and entities that play a role in the event (e.g., a product, the amount of increase in stock price, the main companies involved in a deal). Event processing in financial text has historically been largely knowledge- or pattern-based, relying on manually created rules for matching phrases to events. Other approaches rely on approximate heuristics for automatically gathering event phrases such as the presence of dates or similarity to existing rule-sets. This over-reliance on knowledge-based methods stems from a lack of gold-standard annotated data in the field of financial event processing. Fine-grained sentiment analysis detects which attitude is expressed towards a target entity. Usually, the field is focused on user-generated and opinionated text genres where sentiment is explicitly expressed such as reviews. However, in objective genres such as business news, indirect expressions of implicit sentiment are common. Here, a positive or negative attitude can be inferred by the reader through common sense, connotational world-knowledge. The field of implicit sentiment analysis is currently lacking in fine-grained resources in which the opinion and target entity words are labeled for their implied sentiment value. Financial markets prove to be especially sensitive to news coverage and opinionated reporting. Combining the fine-grained extraction of events and their investor sentiment in company-specific news enables financial applications such as stock forecasting, identifying macro-economic trends, and event studies. Supervised machine learning methods rely on annotated training data, so to enable data-driven, supervised extraction of economic events and implicit sentiment, a substantial amount of annotations is required. We constructed a representative English corpus which was manually annotated with our novel annotation scheme obtaining over 6200 event schemata in 288 company-specific news article for 18 economic types. Next, we annotated the positive, neutral, or negative investor sentiment value on top of these events and added separate opinion and target word annotations, obtaining one of the largest fine-grained targeted datasets with 12,400 sentiment tuples. After verifying the quality of annotations in agreement studies, we applied deep learning models that obtain good performance on comparable tasks to check the portability of these methods to our SENTiVENT dataset in coarse- and fine-grained experiments. For the coarse-grained experiments we preprocessed our token-level annotation to sentences or clauses for event detection or implicit sentiment value classification, which obtained in good results. The fine-grained, token-level extraction of abstract semantic categories such as economic events and implicit sentiment proved to be highly challenging even to advanced current transformer-based transfer-learning methods. We have shown in error analyses our dataset contains larger lexical variation within extracted categories. This highlights a weakness of strictly supervised data-driven approaches: even though our dataset is on par or larger than current reference sets for the fine-grained tasks, knowledge-bases and distantly-supervised methods for instance enhancement and expansion should be introduced to alleviate data scarcity. We concluded that our corpus construction efforts resulted in a qualitative and rich resource that fills the need for data-driven approaches in financial event and implicit sentiment processing.
... In light of these points and concerns, there have been calls for the establishment of a new paradigm for statistical significance to improve statistical research and decisions: see Rao and Lovric (2016). This is particularly important for the big data era where statistical significance based on the conventional criterion is no longer relevant, as Gandomi and Haider (2015) and Algaba et al. (2020) point out. ...