Title: In the World of Big Data, Small Effects Can Still Matter: A Reply to Boyce et al. 2016
Authors: Sandra Matz1, Joe Gladstone2, David Stillwell3
1 Department of Psychology, University of Cambridge, Cambridge, CB2 3EB, UK.
2 UCL School of Management, London, RM NE3, UK
3 Cambridge Judge Business School, University of Cambridge, Cambridge, CB2 1AG, UK
Correspondence to: firstname.lastname@example.org; +447858786958; Department of Psychology,
Downing Street, Cambridge, CB2 3EB, UK.
Keywords: effect size, happiness, consumption, psychological fit, Big Five personality
We make three points in response to Boyce, Daly, Hounkpatin and Wood (2016). First, we
clarify a misunderstanding of the goal of our analyses, which was to investigate the links
between life satisfaction and spending patterns, rather than spending volume. Second, we run
a simulation study to demonstrate that our results are not driven by the proposed statistical
artefact. Finally, we discuss the broader issue of why, in a world of big data, small but reliable
effect sizes can be valuable.
Our goal is to study spending patterns, not spending volume.
Boyce et al. argue that our findings do not provide sufficient evidence for the contention that
spending more money buys happiness, when that money is spent on products and services that
fit a person’s personality. We agree, because this is not the argument we make in the paper.
Our argument is that spending the money one already has on products and services which
match one’s personality (and thus psychological needs) results in greater happiness. That is,
we studied spending patterns (what we buy) rather than spending volume (how much of it we
buy). In fact, we emphasized the relative unimportance of “spending more money” in our
measures, analyses, and study designs. First, we considered the fact that many small
purchases can result in greater happiness than a few large ones (e.g. Nelson and Meyvis,
2008) in the calculation of the person-basket match variable itself. Rather than weighting all
spending categories by the amount spent, we assigned an equal weight to each of them.
Second, we highlighted that the coefficients for income and total spending on life-satisfaction
are non-significant (Table 3, page 6), suggesting that earning or spending more money does
not impact life satisfaction and happiness. Finally, we did not vary the amount spent in our
experiment, but instead focused exclusively on manipulating the spending pattern (i.e.
whether or not the voucher fitted the personality of the recipient).
Our results are not exclusively driven by the proposed statistical artefact.
Boyce et al. (2016) suggest that the effect of the match between customers’ shopping baskets
and their personality might be driven “by participant personality, which is known to relate to
well-being”. We also had this concern. Which is why the original analysis controlled for
participant personality as well as the overall extremity of profiles and found that the effects of
basket-participant matched remained stable when controlling for these variables (see Table 3;
Matz et al., 2016).
To provide further evidence for our effect’s robustness, we ran a simulation on our dataset
that is similar to the one reported by Boyce et al. (2016). In 1,000 iterations, we randomly
allocated the basket personality calculated for each participant in Study 1 to another
participant (i.e., we ‘swap’ participants’ shopping baskets at random). We then calculated the
basket-participant match and ran regression analyses including the control variables used by
Boyce et al. (Model 1 without total spend) and the original control variables of Model 2 (see
online supplementary materials for more details). Out of 1000 iterations, basket-personality
match was significant at an alpha level of 0.05 in only 3.5% of cases when including the
controls used by Boyce et al., and in only 2.3% of cases when including all control variables
of Model 2. The average coefficient of the randomly generated basket-participant match was
B = 0.013 in Model 1 (SD = 0.03; average ß = 0.018; left panel of Figure 1) and B = -0.004 in
Model 2 (SD = 0.03; average β = -0.005; right panel of Figure 1). This compares to
coefficients of B = 0.06 and ß = 0.10 reported for real basket-participant match in our original
analysis (using the same controls). We take this as strong evidence that the relationship
between basket-participant match and life satisfaction is not (or at least not exclusively)
driven by the confounding artefacts suggested by Boyce et al. (2016).
Figure 1. Distribution of regression coefficients (B) for randomly
distributed basket personality across 1,000 iterations, using the
controls of Boyce et al. (left; original Model 1 without total
spend) and the original controls of Model 2 (right).
The importance of small effects.
Boyce et al. (2016) argue that the relationship we report between a consumer’s purchases and
their wellbeing is of no practical relevance. This raises an important debate about the
magnitude of meaningful effect sizes.
Traditional social science research uses small samples (Bertamini & Munafò, 2012; Button et
al., 2013), which require large effect sizes to reach statistical significance and be published.
Large effect sizes are more likely to be replicable (Open Science Collaboration, 2015), but
focusing exclusively on them hinders a nuanced exploration of complex psychological
phenomena such as life satisfaction, which are unlikely to be explained by a few strong
predictors. Instead of dismissing small effect sizes altogether, researchers should explore new
methodologies that enable the discipline of psychology to build a body of small but robust
predictors of behavior. New computational social science approaches (Big Data; see e.g.
Kosinski, Matz, Gosling, Popov, & Stillwell, 2015), for example, make it possible to collect
behavioral data at an unprecedented scale, providing psychologists with opportunities to
identify weak but reliable signals in a complicated world. However, the danger of using these
new methods is that even trivial effects will become statistically significant with large enough
samples. Therefore, how can we distinguish between small effects which are meaningful,
from those which are not?
This requires a scientist’s judgement rather than simply following arbitrary cut-offs. A full
review of situations when small effect sizes are important would require more space than
available in a commentary, but other authors have already discussed some situations. Cortina
and Landis (2009), for example, note that small effects can suggest strong support for a given
phenomenon if they (1) occur in the context of intentionally inauspicious designs, (2)
challenge fundamental theoretical assumptions, and (3) have enormous cumulative
consequences. One illustration of the latter is Abelson’s Paradox (Abelson, 1985).
Investigating the batting performance of major-league baseball players, Abelson showed that
historical batting performance was barely predictive of a player’s performance each time they
stepped up to the batting plate (less than 0.5%). Yet, the cumulative effect over several
hundred bats is so meaningful in practice that it leads to some batters being paid 100,000%
more than others.
In our paper, one challenge in determining the meaning in effect sizes is that it is difficult to
directly compare them across studies with different methodologies, such as self-reported
surveys and objective behavioral data. Study 1 is a ‘Big Data’ field study, where over 76,000
transactions are mined from customers’ bank accounts and where the measurement of
wellbeing is far removed, in both context and time, from when the bank customers’ purchases
were being made. Such a procedure is likely to result in smaller – yet probably more realistic -
effect sizes than panel surveys because they eliminate well-documented response biases (e.g.,
consistency motive, covariation bias, or common method variance). For example, Powdthavee
(2008; cited by Boyce et al., 2016), reports a large effect of social contact on subjective
wellbeing in the British Household Panel Survey. While social contact is surely important for
wellbeing, the reported effect size might be over-estimated because respondents are
subjectively reporting both their social contact and their wellbeing at the same time.
Respondents who felt negatively about their lives, for example, might be less likely to
remember and report short and superficial social contact, such as saying “hello” to a neighbor,
than respondents who felt more positive (mood congruence; Bower, 1981). Indeed, the results
of our Study 2 underline the importance of considering the methodological context when
discussing a given effect size; Study 2’s behavioral field experiment found a medium to large
effect size for the personality-fit interaction (ß = 0.38).
A final consideration when deciding whether a small effect may have practical relevance is
the extent to which the factor can be manipulated. In their commentary, Boyce et al. (2016)
point to other factors that are stronger predictors of wellbeing (in terms of standardized effect
sizes) such as relationships (Powdthavee, 2008), personality (Diener & Lucas, 1999) or stable
employment (McKee-Ryan, Song, Wanberg, & Kinicki, 2005). Such factors certainly play an
important role in predicting life satisfaction. However, personality cannot easily be changed
(McCrae & Costa, 1994) and it is often outside the control of an unemployed person to
arrange for stable employment. Consumption choices, on the other hand, are usually under the
control of the individual and can be changed relatively easily. Even the very poorest groups in
the world (i.e., those living on less than $2 per day), spend substantial amounts on
discretionary goods, such as entertainment, celebrations, clothing and tobacco (Banerjee &
Duflo, 2007). Given that consumption is such a universal phenomenon, even small changes
can have a big impact if they occur on a large scale. A 1% increase in life satisfaction may be
negligible for a single consumer, but if a retail giant like Amazon aimed at making its
customers happier by personalizing their product recommendations, a 1% increase in life
satisfaction across its 244 million customers (Kline, 2014) could turn a small effect size into a
huge social effect.
Psychologists have typically focused on how their findings apply to individuals. However, by
providing the opportunity to understand and influence the behaviors of billions of people
around the world, the era of big data encourages – and possibly requires - us to think bigger.
In this new world, small effects can still matter.
(Cortina & Landis, 2009)
(Boyce, Daly, Hounkpatin, & Wood, n.d.)
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Supplementary Online Material
Simulation Model 1
Simulation Model 2
Total spend (log)
Note. In Model 1 the B-P match predictor reached significance in 35 out of the 1000
iterations. In Model 2 the B-P match predictor reached significant in 23 out of 1000 iterations