• Abstract
• Discussion

Abstract

There is an active debate regarding whether the ego depletion effect is real. A recent preregistered experiment with the Stroop task as the depleting task and the antisaccade task as the outcome task found a medium-level effect size. In the current research, we conducted a preregistered multilab replication of that experiment. Data from 12 labs across the globe (N = 1,775) revealed a small and significant ego depletion effect, d = 0.10. After excluding participants who might have responded randomly during the outcome task, the effect size increased to d = 0.16. By adding an informative, unbiased data point to the literature, our findings contribute to clarifying the existence, size, and generality of ego depletion.

Discussion

In the current multilab collaborating project, we replicated the ego depletion experiment by Dang and colleagues (2017). Preregistered meta-analyses revealed small and significant ego depletion effects on both response accuracy and latency (d = 0.10). After excluding participants who might have responded randomly on the outcome task, the effect size of the accuracy remained the same, but the effect size of the reaction time increased to d = 0.16. This effect size estimate was comparable to another recent endeavor in which Garrison, Finley, and Schmeichel (2019) verified the effectiveness of another depleting task implied by Dang’s (2018) meta-analysis (i.e., the attention essay task, paired with the Stroop task as the outcome measure in Study 1 and with the attention network test as the outcome measure in Study 2) in two preregistered experiments with over 1,000 participants and reported an effect size of d = 0.20. Although these results suggest that the ego depletion effect should be real, the effect sizes might be smaller than previously thought. In order to detect an effect size of 0.10, 0.16, and 0.20 with 80% power (given α = .05, two-tailed), we will need 1,571, 615, and 394 participants per condition, respectively. Does this indicate the true effect size of ego depletion is between 0.10 and 0.20? We suggest the answer is either “yes” or “no.” On the one hand, in the current ego depletion literature (as well as Hagger et al.’s and our replications), most studies adopted very brief depletion manipulations that were generally less than 10 min. Participants’ responses to these weak manipulations could vary to a great extent, with some participants feeling exhausted while others feeling indifferent or even excited as such tasks may serve to “warm-up” their self-control (e.g., Lopez, Courtney, & Wagner, 2019; Wenzel, Rowland, Zahn, & Kubiak, 2019). Therefore, there is a substantive heterogeneity in the size of ego depletion in the literature and the average effect size is small (e.g., between 0.10 and 0.20). If we continue with these weak manipulations, the answer is more likely to be yes. On the other hand, if stronger manipulations were implemented, the answer should be more likely to be no and the effect size should be increased as the strength of the manipulation increases. Consistently with this proposition, recent evidence showed that the depletion intensity is positively correlated with subsequent fatigue perception (Tsai & Li, 2019). When the manipulation lasted for 1 hr or more, the effect size increased from medium to large (Radel, Gruet, & Barzykowski, 2019; Sjåstad & Baumeister, 2018). Future studies need to systematically test the dose-dependent feature of ego depletion. In addition, in line with Job et al. (2010), in the full sample, the current project found supporting evidence on the RT for the moderating effect of lay theory about willpower such that people with an unlimited-resource theory were influenced less by the depletion manipulation. Relatedly, a group of studies recently reported reversed ego depletion in individuals who believed that initial exertion is energizing (Savani & Job, 2017). However, after excluding participants who might have responded randomly, which might lead to a more accurate measure of the RT, the moderating effect of lay theory about willpower disappeared. The lack of robustness, in combination with the fact that lay theories did not moderate the effect on error rates, indicates that our results do not provide unambiguous support for a moderating role of lay theories of willpower. Finally, since our main purpose was to test whether the ego depletion effect is replicable, the current research provides little evidence regarding the mechanisms underlying ego depletion. The observed performance decline after initial exertion may result from insufficient resource for subsequent acts of self-control (Baumeister et al., 2007) or from reduced motivation to exert further control (Inzlicht & Schmeichel, 2012). However, our results pave the way for further theoretical analyses and related empirical examinations because after all it will be meaningless to debate why there is such a phenomenon if the phenomenon itself cannot be observed.