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Comparison of PubMed, Scopus, Web of Science, and Google Scholar: Strengths and weaknesses

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  • North West London Deanery

Abstract

The evolution of the electronic age has led to the development of numerous medical databases on the World Wide Web, offering search facilities on a particular subject and the ability to perform citation analysis. We compared the content coverage and practical utility of PubMed, Scopus, Web of Science, and Google Scholar. The official Web pages of the databases were used to extract information on the range of journals covered, search facilities and restrictions, and update frequency. We used the example of a keyword search to evaluate the usefulness of these databases in biomedical information retrieval and a specific published article to evaluate their utility in performing citation analysis. All databases were practical in use and offered numerous search facilities. PubMed and Google Scholar are accessed for free. The keyword search with PubMed offers optimal update frequency and includes online early articles; other databases can rate articles by number of citations, as an index of importance. For citation analysis, Scopus offers about 20% more coverage than Web of Science, whereas Google Scholar offers results of inconsistent accuracy. PubMed remains an optimal tool in biomedical electronic research. Scopus covers a wider journal range, of help both in keyword searching and citation analysis, but it is currently limited to recent articles (published after 1995) compared with Web of Science. Google Scholar, as for the Web in general, can help in the retrieval of even the most obscure information but its use is marred by inadequate, less often updated, citation information.
The FASEB Journal Life Sciences Forum
Comparison of PubMed, Scopus, Web of Science, and
Google Scholar: strengths and weaknesses
Matthew E. Falagas,*
,†,1
Eleni I. Pitsouni,* George A. Malietzis,* and Georgios Pappas
*Alfa Institute of Biomedical Sciences, Athens, Greece;
Department of Medicine, Tufts University
School of Medicine, Boston, Massachusetts, USA; and
Institute of Continuing Medical Education of
Ioannina, Ioannina, Greece
ABSTRACT The evolution of the electronic age has
led to the development of numerous medical databases
on the World Wide Web, offering search facilities on a
particular subject and the ability to perform citation
analysis. We compared the content coverage and prac-
tical utility of PubMed, Scopus, Web of Science, and
Google Scholar. The official Web pages of the data-
bases were used to extract information on the range of
journals covered, search facilities and restrictions, and
update frequency. We used the example of a keyword
search to evaluate the usefulness of these databases in
biomedical information retrieval and a specific pub-
lished article to evaluate their utility in performing
citation analysis. All databases were practical in use and
offered numerous search facilities. PubMed and
Google Scholar are accessed for free. The keyword
search with PubMed offers optimal update frequency
and includes online early articles; other databases can
rate articles by number of citations, as an index of
importance. For citation analysis, Scopus offers about
20% more coverage than Web of Science, whereas
Google Scholar offers results of inconsistent accuracy.
PubMed remains an optimal tool in biomedical elec-
tronic research. Scopus covers a wider journal range, of
help both in keyword searching and citation analysis,
but it is currently limited to recent articles (published
after 1995) compared with Web of Science. Google
Scholar, as for the Web in general, can help in the
retrieval of even the most obscure information but its
use is marred by inadequate, less often updated, cita-
tion information.—Falagas, M. E., Pitsouni, E I., Mali-
etzis, G. A., and Pappas, G. Comparison of Pub Med,
Scopus, Web of Science, and Google Scholar: strengths
and weaknesses. FASEB J. 22, 338–342 (2008)
Key Words: citation analysis open access Medline Insti-
tute of Scientific Information (ISI) education electronic da-
tabases
The development along with the spread of the
World Wide Web (WWW) represents an informational
revolution, with rapid, practical distribution and stor-
age of data available worldwide. One of the most
prominent examples of enhanced storage and distribu-
tion of important information is the development of
scientific databases, the significance of which was rec-
ognized early. Specifically in the field of medicine, the
National Library of Medicine (NLM) in the United
States introduced the first interactive searchable data-
base (Medline) in 1971 (1) and subsequently in 1996
(1) added the “Old Medline” database with coverage of
publications between 1950 and 1965. In 1997, PubMed
(a combination of both Old Medline and Medline) was
launched to the Internet by NLM and has become the
most popular and one of the most reliable WWW
resources for clinicians and researchers.
Another acknowledged source of scientific informa-
tion is the Institute of Scientific Information (ISI) of
Thomson Scientific, which has been serving as a data
provider since the early 1960s (2), especially for citation
analyses. In recent years electronic database searching
has become the de facto mode of medical information
retrieval, as shown by numerous studies highlighting
the utility of the WWW in medicine today (3–7). As
expected, numerous efforts have focused on refining
the mode of information retrieval and augmenting
citation analysis. In that vein in 2004, Scopus and
Google Scholar databases were also launched to the
Internet. Given that the various scientific databases
have their own characteristics, we aimed in this
article to compare the utility of the current most
popular sources of scientific information in biomed-
ical sciences, namely PubMed, Scopus, Web of Sci-
ence, and Google Scholar, in retrieval of information
on a specific biomedical subject and in up-to-date
citation analysis.
MATERIALS AND METHODS
We searched the official home pages of PubMed, Scopus,
Web of Science, and Google Scholar to identify and extract
information regarding the various characteristics of these
databases. We focused on the date of the official inaugura-
tion, content, coverage, number of keywords allowed for each
search, uses, updating, owner, and characteristics and quality
of citations in our analysis of PubMed, Scopus, Web of
Science, and Google Scholar.
1
Correspondence: Alfa Institute of Biomedical Sciences
(AIBS), 9 Neapoleos St., 151 23 Marousi, Greece. E-mail:
m.falagas@aibs.gr
doi: 10.1096/fj.07-9492LSF
338 0892-6638/08/0022-0338 © FASEB
Furthermore, we evaluated the utility of these databases in
retrieving information on a particular subject 1) by using a
specific keyword referring to a well-defined medical condition
(we chose the term “brucellosis” as being specific enough as
a condition and a medical concept that is not too vague) and
2) by attempting to perform a citation analysis for a specific
recent article. A recent article from a highly cited journal was
chosen to assure that referencing to the article would be
constant in the present period (the article used was Pappas,
G., Akritidis, N., Bosilkovski, M., and Tsianos, E. (2005)
Brucellosis. N. Engl. J. Med. 352, 2325–2336). The keyword
search was repeated daily for all databases to estimate update
speed. The article’s citation analysis was followed through
Google Scholar, Scopus, and Web of Science for a period of
2 months.
The search for the identification of relevant information
and the extraction of data was performed by two of the
authors independently (E.I.P. and G.A.M.). Any discrepan-
cies were discussed in meetings with the senior author
(M.E.F.). The evaluation of utility of the databases for a
specific keyword search and a specific article was performed
by G.P.
RESULTS
General characteristics of the databases
In Table 1 we present data regarding various character-
istics of PubMed, Scopus, Web of Science, and Google
Scholar. Scopus is the database that indexes a larger
number of journals than the other three databases
studied. Web of Science does not provide any data
regarding open access articles that it includes (if any).
PubMed, Google Scholar, and Web of Science origi-
nate from the United States, whereas Scopus originates
from Europe. PubMed and Google Scholar are free and
provide open access to all interested clinicians, re-
searchers, and trainees and also to the public in gen-
eral. Scopus and Web of Science are databases that
belong to commercial providers and require an access
fee. Regarding Google Scholar, although relevant data
are not summarized anywhere, the database is essen-
tially a part of a popular WWW search engine, which
means that there are no limits on the languages cov-
ered, keywords allowed per search, and list of covered
journals, provided for the latter that an electronic
edition exists. Similarly there are no data for the
frequency of Google Scholar updates (see later discus-
sion of this topic).
PubMed focuses mainly on medicine and biomedical
sciences, whereas Scopus, Web of Science, and Google
Scholar cover most scientific fields. Web of Science
covers the oldest publications, because its indexed and
archived records go back to 1900. PubMed allows the
larger number of keywords per search but is the only
database of the four that does not provide citation
analysis. Scopus includes articles published from 1966
on, but information regarding citation analysis is avail-
able only for articles published after 1996.
PubMed was developed by the NLM, a division of the
National Institutes of Health, and rapidly became syn-
onymous with medical literature research worldwide. It
offers a quick free search with numerous keywords as
well as limited searching with various criteria [i.e.,
search by authors, journal, date of publication, date of
addition to PubMed, or type of article]. The results of
a search can be displayed in a listing including from
5–500 items per page or as a summary [in which the full
title, the names of the authors, the source and PubMed
identification (PMID) of each article are presented],
and the list can also be presented with abstracts, if
available. Information on whether an abstract is avail-
able, and free text access is comprehensively repre-
sented by a displayed icon. A search can easily be sent
to text, a file, the clipboard, e-mail, an RSS feed, and an
order. PubMed also allows for direct use of other search
engines developed by the NLM, such as GENSAT,
OMIM, and PMC, the latter allowing for free full text
access to a wide array of previous decades’ publications
from numerous journals. Thus, PubMed now offers 1
million freely available articles of which a significant
number come from digitized back issues.
One major advantage of PubMed, not reproduced by
Scopus or Web of Science, is that it is readily updated
not only with printed literature but also with literature
that has been presented online in an early version
before print publication by various journals. In con-
trast, Scopus and Web of Science are readily updated
for printed literature but do not include online early
versions.
The Scopus database was developed by Elsevier,
combining the characteristics of both PubMed and
Web of Science. These combined characteristics allow
for enhanced utility, both for medical literature re-
search and academic needs (citation analysis), yet ac-
cess to the database is not free, although reviewers for
numerous Elsevier medical journals are entitled to 1
month of free use. It offers a quick search, a basic
search, an author search, an advanced search, and a
source search. In the basic search the results for the
keywords chosen can be limited by date of publishing,
by addition to Scopus, by document type, and by
subject areas, whereas the author search is based only
on author names. The advanced search combines the
basic search without the limits and the author search,
and more operators and codes are allowed. The source
search is confined to selection of a subject area, a
source type (i.e., trade publication or conference pro-
ceedings), a source title, the ISSN number, and the
publisher.
The search results in Scopus can be displayed as a
listing of 20–200 items per page, and documents can be
saved to a list and/or can be exported, printed, or
e-mailed. The results can be refined by source title,
author name, year of publication, document type,
and/or subject area, and a new search can be initiated
within the results. The presence of an abstract, refer-
ences, and free full text is noted under each article title,
in addition to where these can be found. When ab-
stracts are displayed, the keywords are highlighted. The
fields that can be included in the output are optional
(i.e., citation information, bibliographical information,
339SCIENTIFIC DATABASES, PROS AND CONS
abstract, and keywords). The citation analysis that Sco-
pus performs is presented as a table with numbers of
cited articles for individual years, as well as the total
number of cited references for all years. The articles
cited can be accessed by simply clicking on the number
of citations. In addition, Scopus has search tips written
in 10 languages.
Web of Science was developed by Thomson Scien-
tific, a part of the Thomson Corporation, another
private company, and has dominated the field of aca-
TABLE 1. Characteristics of databases
Characteristic Pub Med Scopus Web of Science Google Scholar
Date of official
inauguration
06/1997
a
11/2004 2004
b
11/2004
Content
No. of journals 6000 (827 open access) 12,850 (500 open
access)
8700 No data provided
(theoretically all
electronic resources)
Languages English (plus 56 other
languages)
English (plus more
than 30 other
languages)
English (plus 45
other languages)
English (plus any language)
Focus (field) Core clinical journals, dental
journals, nursing journals,
biomedicine, medicine,
history of medicine,
bioethics, space, life
sciences
Physical sciences,
health sciences,
life sciences,
social sciences
Science, technology,
social sciences, arts
and humanities
Biology, life sciences and
environmental sciences,
business, administration,
finance and economics,
chemistry and materials
science, engineering,
pharmacology, veterinary
science, social sciences,
arts and humanities
Period covered 1950–present 1966–present 1900–present Theoretically all available
electronically
Databases
covered
Medline (1966–present), old
Medline (1950–1965),
PubMed Central, linked to
other, more specialized,
NLM databases
100% Medline,
Embase,
Compendex,
World textile
index, Fluidex,
Geobase,
Biobase
Science citation index
expanded, social
sciences citation
index, arts and
humanities citation
index, index
chemistry, current
chemical reactions
PubMed, OCLC First
Search
No. of
keywords
allowed
No limit 30 15 Theoretically no limit
Search
Abstracts ()()()()
Authors ()()()()
Citations ()()()()
Patents ()()()()
Uses Links to related articles,
links to full-text (5426
journals), links to free full
text articles for a subset of
journals (827 open access
journals)
Links to full-text
articles and
other library
resources
Links to full-text,
links to related
articles
Links to full-text articles,
free full-text articles, links
to journals, links to
related articles, links to
libraries
Updating Daily 1–2 times weekly Weekly Monthly on average
Developer/owner
(country)
National Center for
Biotechnology
Information (NCBI), NLM
(US)
Elsevier
(Netherlands)
Thomson Scientific
and Health Care
Corporation (US)
Google Inc. (US)
Citation analysis None Total number of
articles citing
work on a topic
or by an
individual
author
As for Web of Science
plus the total
number of articles
on a topic or by an
individual author
cited in other
articles
Next to each paper listed is
a “cited by” link; clicking
on this link shows the
citation analysis
a
PubMed was created by the NLM of the United States with the intention of making the content of Medline accessible via the Internet.
b
Web of Science was created by Thomson Scientific to make citation indices (that E. Garfield assessed since the early 1960s) accessible via the
Internet.
340 Vol. 22 February 2008 FALAGAS ET AL.The FASEB Journal
demic reference, mainly through the annual release of
the journal impact factor, a tool for evaluating the
importance and influence of specific publications. The
impact factor has been highly criticized but remains the
most widely used of the indexes available. It has a quick
search (by entering a topic), an advanced search, a
general search, and a cited reference search. Help is
offered for all types of searches of author, of group
author, and of full source title, as well as of abbrevi-
ations. In the cited reference search the search can
be limited by cited author, cited work, and cited
years, whereas the cited author index and the cited
work index can be presented, if the researcher
requires it.
The results of a search can be displayed as a listing of
10–50 items per page. The full title, author names, and
source are provided. When the full text is available, the
option of “view free full text” is present. Related records
can be found, sorted by latest date, times cited, rele-
vance, first author, publication year, and source title.
The results can be analyzed (i.e., by author, country/
territory, or document type), and the citation report is
presented with a label bar chart. The results can be
refined, and the researcher can view or exclude records.
Google Scholar was developed by Google Inc., an-
other private company, but it is freely accessible and
aims to summarize all electronic references on a sub-
ject. There is no journal frame/list available for Google
Scholar, because it presumably lists all publications that
have emerged from the electronic search. Being essen-
tially a Web search engine, its aim is to reach the widest
audience available. It allows a quick search and an
advanced search. In the advanced search the results can
be limited by title words, authors, source, date of
publication, and subject areas. The languages of the
interface and of the search are optional. The results can
be displayed as a listing of 10–300 items per page. Each
retrieved article is represented by title, authors, and
source, but the abstract and information on free full
text availability are not provided by Google Scholar.
Under each retrieved article the number of cited
articles is noted and can be retrieved by clicking on the
relevant link. By clicking on the article title, Google
Scholar leads you to a list of possible links to the article,
usually on the journal’s site, but for older articles the
link is directed to the PubMed citation. In addition,
Google Scholar provides links to relevant articles and
allows for a general Google Web search, using self-
selected keywords from the article and the author name.
Utility trial
A search on the word “brucellosis” elicits thousands of
results by all of the databases. PubMed’s simple search
elicits the newest ones first and PubMed is updated
daily, including online early articles, thus allowing for a
comprehensive follow-up of a specific subject. On the
other hand, some of the results returned (roughly 5%)
were of peripheral relevance to the subject (a kind of
false-positive result). Relevant articles (as categorized
by PubMed) can also be assessed. Unfortunately, the
relevance is inconsistent. Updates to Scopus and Web
of Science were less frequent, generally on a weekly
basis. The results produced by Scopus corresponded to
its extended listing of included journals with a greater
number of citations. False-positive results in Scopus
could be eliminated if one is searching for articles
including the keyword in the title only, but that search
omitted a few relevant articles (an analog to false-
negative results). By clicking on the head of the rele-
vant column, articles can be rearranged by most cited
in declining order, thus allowing the uninitiated
searcher to familiarize himself or herself with the
outstanding articles on the subject. PubMed does not
possess such a facility. Google Scholar presents results
with the most cited first. Although online early articles
are included, updates are less frequent (in a period
certainly exceeding 1 month).
Searching for citations of a specific article can be a
difficult task for academic candidates, and the task is
even more difficult when the question of which journal
citations are eligible is raised. The use of Web of
Science has been the standard, yet Scopus does offer
more citation analyses; in our case, Scopus listed 20%
more articles referencing our example in any given
period than did Web of Science. Admittedly, some of
these additional citations were derived from vague
journals in non-English languages, yet even Web of
Science lists similar journals. The inclusion criteria of
Web of Science, similar to the criteria used for calcu-
lating the impact factor, have repeatedly been the
subject of dispute (8). Both databases include only
published articles and not online early ones. One major
factor that may bias these results though is the selection
of a recent article as an example. If an older article
were chosen, Scopus would offer limited citation infor-
mation, because it covers a significantly shorter period
than Web of Science. This observation has also been
confirmed in a previous comparison of the three cita-
tion databases (9). The use of Google Scholar to
determine citations for the particular article was disap-
pointing. The reference list was much shorter than
those for the other databases and, as mentioned earlier,
updates was less frequent. It was obvious that Google
Scholar only cited articles that were accessible electron-
ically accessible. When we assessed articles for other
examples, duplicate references (false-positive citations)
were a common occurrence.
A final interesting observation was that citation anal-
ysis could be adequately updated when Google was
used, with article year/volume/page numbers as key-
word. In that way, most online early articles were
rapidly identified, although the vast number of results
prohibits any adequate citation analysis to be performed.
DISCUSSION
A critical review of the information we were able to
collect regarding the four sources of scientific informa-
341SCIENTIFIC DATABASES, PROS AND CONS
tion that we focused on suggests the following conclu-
sions. PubMed is a very handy, quick, and easy to use
database. Its practicality in use, the fact that it is free,
and the authority it has gained through the years have
made it the most frequently used resource for informa-
tion in the biomedical field.
Scopus includes a more expanded spectrum of jour-
nals than PubMed and Web of Science, and its citation
analysis is faster and includes more articles than the
citation analysis of Web of Science. On the other hand,
the citation analysis that Web of Science presents
provides better graphics and is more detailed than the
citation analysis of Scopus, probably because Web of
Science has been designed with the intention of satis-
fying users in citation analysis, a field discussed and
debated by scientists for decades.
There is a debate in the scientific community on
Google Scholar is a database that should be used by
clinicians (10, 11), because of its inadequacies (12, 13)
and the fact that much information about its content
coverage remains unknown. Results with Google
Scholar are displayed in relation to times of visits from
users, not in relation to another index of quality of the
publication.
Google Scholar presents all the benefits and draw-
backs of the WWW. It sometimes offers unique options
in the scientific field (10, 14): in our example, using its
Web search option, a free full text of the article could
be retrieved from various Web sites, whereas other
databases and the journal itself did not offer free access
at the moment. The access may possibly be illegal, but
this is a characteristic of the WWW: information is
ample, but access is often uncontrolled. The need for a
systematic reconstitution of the pros and cons of each
database and the development of a formula for free
access to such a powerful database apart from PubMed
seems warranted.
In conclusion, scientific databases of biomedical in-
formation are frequently used by both clinicians and
researches. In this article, we compared the content
and various practical aspects in the utility of the main
databases of biomedical scientific information. We
found that PubMed remains an important resource for
clinicians and researchers, Scopus covers a wider jour-
nal range and offer the capability for citation analysis
[currently limited to recent articles (published after
1995) compared with Web of Science], and Google
Scholar can help in the retrieval of even the most
oblique information, but is marred by inadequate, less
often updated, citation information
M.E.F. had the idea for this article. M.E.F. and G.P.
developed the methodology used. E.I.P., G.A.M., and G.P.
identified the relevant data. M.E.F. and E.I.P. wrote the first
draft of the manuscript that was revised extensively by G.P. All
authors participated in subsequent revisions of the manu-
script and approved its final version. M.E.F. is the guarantor.
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342 Vol. 22 February 2008 FALAGAS ET AL.The FASEB Journal
... Considering that the outcomes of the bibliographic research may vary according to the use of different literature databases, studies focusing on comparative research should use such databases with utmost awareness [46]. In this perspective, Falagas et al. [47] remarked "For citation analysis, Scopus offers about 20% more coverage than Web of Science, whereas Google Scholar offers results of inconsistent ...
... Considering that the outcomes of the bibliographic research may vary according to the use of different literature databases, studies focusing on comparative research should use such databases with utmost awareness [46]. In this perspective, Falagas et al. [47] remarked "For citation analysis, Scopus offers about 20% more coverage than Web of Science, whereas Google Scholar offers results of inconsistent accuracy" [47]. The same authors also stated "Google Scholar as for the Web in general, can help in the retrieval of even the most obscure information but its use is marred by inadequate, less often updated, citation information" [47]. ...
... Considering that the outcomes of the bibliographic research may vary according to the use of different literature databases, studies focusing on comparative research should use such databases with utmost awareness [46]. In this perspective, Falagas et al. [47] remarked "For citation analysis, Scopus offers about 20% more coverage than Web of Science, whereas Google Scholar offers results of inconsistent accuracy" [47]. The same authors also stated "Google Scholar as for the Web in general, can help in the retrieval of even the most obscure information but its use is marred by inadequate, less often updated, citation information" [47]. ...
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... In the literature, it is possible to find different articles that analyze academic databases, as in [15]- [19]. However, none of these works specifically analyzed the area of Engineering and Computing Education; hence, the differential of our paper is to analyze these databases from the perspective of this area. ...
... Web of Science and Scopus are the most comprehensive databases containing different types of publications includ- ing journal articles, books, book chapters and conference proceedings, and they are very diverse in terms of the journals and disciplines covered (e.g., social sciences, humanities, life sciences and physical sciences) [45]. We are cognisant of the critiques levelled against Google Scholar as a reliable database for literature reviews [45,46], particularly its use as the principal search engine [47]. Although Google Scholar has numerous limitations, it provided relevant publications that could not be retrieved from other databases consistent with assertions by Falagas et al. [45]. ...
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