We strongly overestimate the power of self-interest on others' blood donation willingness and smoking policies

Self-interest Is Overestimated: Two Successful Pre-registered Replications and Extensions of Miller and Ratner (1998). Cameron Brick et al. Collabra: Psychology (2021) 7 (1): 23443, May 2021. https://doi.org/10.1525/collabra.23443

Abstract: Self-interest is a central driver of attitudes and behaviors, but people also act against their immediate self-interest through prosocial behaviors, voting incongruously with their finances, or punishing others at personal cost. How much people believe that self-interest causes attitudes and behaviors is important, because this belief may shape regulation, shared narratives, and institutional structures. An influential paper claimed that people overestimate the power of self-interest on others’ attitudes and behavioral intentions (Miller & Ratner, 1998). We present two registered, close, and successful replications (U.S. MTurk, N = 800; U.K. Prolific, N = 799) that compared actual to estimated intentions, with open data and code. Consistent with the original article, participants overestimated the impact of payment on blood donation in Study 1, ds = 0.59 [0.51, 0.66], 0.57 [0.49, 0.64], and overestimated the importance of smoking status for smoking policy preferences in Study 4, ds = 0.75 [0.59, 0.90], 0.84 [0.73, 0.96]. These replications included two extensions: 1) communal orientation as a moderator of overestimation and 2) a more detailed measure of self-interest in Study 4 (ordinal smoking status). Communal orientation did not predict overestimation, and the ordinal smoking measure yielded similar results to the main study. Verifying the overestimation error informs behavioral theories across several fields and has practical implications for institutions that require trust and cooperation. All materials, data, and code are available at osf.io/57mdc/

Keywords: self-interest, judgment, bias, decision making, attribution, pre-registered replication

General Discussion

The results in both samples and both studies strongly supported the original findings. Individuals overestimated the impact of self-interest on intentions to donate blood, and also how much smoking status determined support of smoking regulations (ds > 0.58). The overestimation effects may have been smaller than the original paper, but original effect sizes could not be precisely calculated because the variances were not reported. Any discrepancies in effect size from the original could be attributed to noise from their small sample size, an estimation error due to the lack of their reported statistics, or differences in the context or manipulation strength. For example, because of currency inflation, $15 was less incentive in 2019 than in 1998, which could lead to smaller perceived incentive in the replication.

In Study 4, the original study did not find significant effects of self-interest for four out of eight policies in self-ratings, perhaps due to lack of statistical power. We found support for self-interest effects for 13 out of 16 tests (smokers endorsed the policies less; eight policies in two samples), with particularly large effects in the MTurk sample (Table S4). Replications often focus on replicating the significant original effects, but finding support for non-significant effects in the original article is also informative (Chandrashekar et al., 2020; LeBel et al., 2019). Here, these additional findings suggest strong generalizability of the overestimation effect across different types of smoking policies (e.g., restriction and taxation).

To evaluate a more granular measure of self-interest, a random half of participants in a Study 4 extension gave responses for five categories of smoking frequency rather than just two. The ordinal smoking status scale did not yield enough smokers within each category for inferential tests. However, it appears from visual analysis that overestimation may be most pronounced when individuals consider others with stronger vested interests. In the extension, that pattern could be partially due to an expectancy effect. Participants may have assumed that being asked about multiple categories of smoker implied that each category would be different in policy support.

The other extension investigated individual differences that predict overestimation. The social norm in Western individualistic cultures that self-interest powerfully determines behavior may be relevant to overestimation (Ratner & Miller, 2001). Beliefs about self-interest may become self-fulfilling by influencing social institutions and individual decision-making processes, which in turn could reinforce the original idea of self-interested human nature. Therefore, communalism was tested in predicting donation, policy support, estimates of each, and overestimation of self-interest. As expected, communality was positively associated with more prosocial behavior and endorsement of smoking restrictions, and was also positively associated with higher estimates of others' prosociality in both studies. However, we found no support for a relationship between overestimation and communality in either study. Exploratory correlations with other demographics revealed mostly null effects, but being younger was associated with more overestimation in Study 1, perhaps because younger individuals have less money. It remains valuable to identify other individual differences associated with overestimation.

Limitations and Future Directions

Alternative Explanations

Self-reported willingness to donate blood or endorse smoking policies is not equivalent to objective behaviors like blood donation or voting. The main narrative in this paper is that people over-estimate others' self-interest, but the results are also consistent with the pattern that such estimates are accurate and that self-reported willingness is inaccurate; that in actual behavior people would manifest more self-interest than they expect or are willing to report. Further studies with observed behavior would be valuable for testing this account.

The experimental paradigms were copied from the original manuscript and not validated before testing the hypotheses. The vignettes and manipulations might have confounds or unknown effects orthogonal to the theory and predictions used here. Additionally, the participants were only given very sparse information about the targets, e.g., that they were smokers or nonsmokers. This could have created an expectancy effect or at the least an ecologically unusual focus on a single attribute when predicting how individuals would evaluate policies. By failing to provide rich, complex targets with varied mental experiences, the paradigms here may have encouraged individuals to focus on external behaviors like smoking, which could alter attributions and perceived self-interest (Vuolevi & Van Lange, 2009). Future studies could consider richer, more life-like vignettes, or paying participants for their accuracy.

Attitudes versus Behaviors

The original article and the current replications hinge on outcomes that may be better characterized as intentions rather than behaviors. This is important because self-interest may predict behavior better than attitudes (Ratner & Miller, 2001). For instance, one study found that people who owned property or had school-age children did not oppose school busing policy more than those without material stake in the policy, but they were much more likely to join anti-busing organizations (Green & Cowden, 1992). Another key paper found that people overestimated their likelihood of acting generously but accurately predicted other's behaviors (Epley & Dunning, 2000). Perceived self-interest may be higher when people face immediate, concrete outcomes (Boninger et al., 1995), and people's sensitivity to their self-interest increases after self-interest is made salient (Ratner & Miller, 2001). Thus, future research on the overestimation of self-interest could focus on consequential behaviors rather than hypotheticals. This could help resolve conflicting findings (Epley & Dunning, 2000; Vuolevi & Van Lange, 2009) and provide better generalizability to real-world contexts.

Constraints on Generality

The current findings and their interpretation are based on sampling and measurement choices that limit their generalizability as with any study (Simons et al., 2017).

Sample. The participants were recruited from MTurk (USA) and Prolific (UK). Both samples were more representative of their countries than university student samples, but the results may have limited generalizability to populations that are not Western, Educated, Industrialized, Rich, and Democratic (Cheon et al., 2020; Henrich et al., 2010). In particular, overestimation of others' self-interest may be inflated by social norms of self-interest in individualistic societies. There is a strong need for studies on overestimation of others' self-interests in non-Western samples. Cross-cultural, multi-lab studies such as through consortia like the Psychological Science Accelerator (Moshontz et al., 2018) could replicate and extend this phenomenon particularly in collectivistic cultures with weaker norms of self-interest.

Method, Measures, and Contexts. We closely replicated the original studies across two medical topics—blood donation and smoking—measuring attitudes and intentions but not objective behavior. Our results appeared to contradict Epley & Dunning (2000), but were consistent with Vuolevi & Van Lange (2009), which both measured behavior. These discrepancies could be due to differences in measures or topics. Future replication studies could focus on consequential behaviors and consider other decision contexts such as financial or environmental decisions.

Overestimating self-interest may also be higher when participants lack information about the other people making decisions. When study vignettes refer to unspecified others and only provide limited information, e.g., the decision maker is a smoker or not, participants may base their estimates on generalized perceptions of norms of self-interest (Vuolevi & Van Lange, 2009). Therefore, future studies could investigate contexts in which participants have more specific information or richer interactions with the estimation targets.

Additionally, there was a possible ceiling effect in self-reported policy endorsement in Study 4. This could have led to an artificially smaller difference between estimates and self-reported preferences due to the specific policies. That is, for a different set of policies, one might observe even more overestimation without this restriction in range.