We conducted preregistered replications of 28 classic and contemporary published findings, with protocols that were peer reviewed in advance, to examine variation in effect magnitudes across samples and settings. Each protocol was administered to approximately half of 125 samples that comprised 15,305 participants from 36 countries and territories. Using the conventional criterion of statistical significance ( p < .05), we found that 15 (54%) of the replications provided evidence of a statistically significant effect in the same direction as the original finding. With a strict significance criterion ( p < .0001), 14 (50%) of the replications still provided such evidence, a reflection of the extremely high-powered design. Seven (25%) of the replications yielded effect sizes larger than the original ones, and 21 (75%) yielded effect sizes smaller than the original ones. The median comparable Cohen’s ds were 0.60 for the original findings and 0.15 for the replications. The effect sizes were small (< 0.20) in 16 of the replications (57%), and 9 effects (32%) were in the direction opposite the direction of the original effect. Across settings, the Q statistic indicated significant heterogeneity in 11 (39%) of the replication effects, and most of those were among the findings with the largest overall effect sizes; only 1 effect that was near zero in the aggregate showed significant heterogeneity according to this measure. Only 1 effect had a tau value greater than .20, an indication of moderate heterogeneity. Eight others had tau values near or slightly above .10, an indication of slight heterogeneity. Moderation tests indicated that very little heterogeneity was attributable to the order in which the tasks were performed or whether the tasks were administered in lab versus online. Exploratory comparisons revealed little heterogeneity between Western, educated, industrialized, rich, and democratic (WEIRD) cultures and less WEIRD cultures (i.e., cultures with relatively high and low WEIRDness scores, respectively). Cumulatively, variability in the observed effect sizes was attributable more to the effect being studied than to the sample or setting in which it was studied.

Previous research has documented the consequences of feeling fused with a group; here we examine the nature of identity fusion. Specifically, we sought to determine what fusion is and the mediating mechanisms that lead fused individuals to make extraordinary sacrifices for their group. Guided by the assumption that fusion emphasizes the extent to which people develop relational ties to the group, we developed a measure designed to capture feelings of connectedness and reciprocal strength with the group. In 10 studies, the newly developed scale displayed predicted relationships with related measures, including an earlier (pictorial) measure of fusion and a measure of group identification. Also as expected, fusion scores were independent of several measures of personality and identity. Moreover, the scale predicted endorsement of extreme progroup behaviors with greater fidelity than did an earlier pictorial measure of identity fusion, which was, in turn, superior to a measure of group identification. Earlier evidence that the personal and social selves of fused persons are functionally equivalent was replicated, and it was shown that feelings of agency and invulnerability mediated the effects of fusion on extreme behavior. Finally, Spanish- and English-language versions of the verbal fusion scale showed similar factor structure as well as evidence of convergent, discriminant, and predictive validity in samples of Spaniards and Americans, as well as immigrants from 22 different countries. This work advances a new perspective on the interplay between social and personal identity.

We sought to identify the mechanisms that cause strongly fused individuals (those who have a powerful, visceral feeling of oneness with the group) to make extreme sacrifices for their group. A large multinational study revealed a widespread tendency for fused individuals to endorse making extreme sacrifices for their country. Nevertheless, when asked which of several groups they were most inclined to die for, most participants favored relatively small groups, such as family, over a large and extended group, such as country (Study 1). To integrate these findings, we proposed that a common mechanism accounts for the willingness of fused people to die for smaller and larger groups. Specifically, when fused people perceive that group members share core characteristics, they are more likely to project familial ties common in smaller groups onto the extended group, and this enhances willingness to fight and die for the larger group. Consistent with this, encouraging fused persons to focus on shared core characteristics of members of their country increased their endorsement of making extreme sacrifices for their country. This pattern emerged whether the core characteristics were biological (Studies 2 and 3) or psychological (Studies 4-6) and whether participants were from China, India, the United States, or Spain. Further, priming shared core values increased the perception of familial ties among fused group members, which, in turn, mediated the influence of fusion on endorsement of extreme sacrifices for the country (Study 5). Study 6 replicated this moderated mediation effect whether the core characteristics were positive or negative. Apparently, for strongly fused persons, recognizing that other group members share core characteristics makes extended groups seem "family like" and worth dying for.

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We conducted preregistered replications of 28 classic and contemporary published findings with protocols that were peer reviewed in advance to examine variation in effect magnitudes across sample and setting. Each protocol was administered to approximately half of 125 samples and 15,305 total participants from 36 countries and territories. Using conventional statistical significance (p &lt; .05), fifteen (54%) of the replications provided evidence in the same direction and statistically significant as the original finding. With a strict significance criterion (p &lt; .0001), fourteen (50%) provide such evidence reflecting the extremely high powered design. Seven (25%) of the replications had effect sizes larger than the original finding and 21 (75%) had effect sizes smaller than the original finding. The median comparable Cohen’s d effect sizes for original findings was 0.60 and for replications was 0.15. Sixteen replications (57%) had small effect sizes (&lt; .20) and 9 (32%) were in the opposite direction from the original finding. Across settings, 11 (39%) showed significant heterogeneity using the Q statistic and most of those were among the findings eliciting the largest overall effect sizes; only one effect that was near zero in the aggregate showed significant heterogeneity. Only one effect showed a Tau &gt; 0.20 indicating moderate heterogeneity. Nine others had a Tau near or slightly above 0.10 indicating slight heterogeneity. In moderation tests, very little heterogeneity was attributable to task order, administration in lab versus online, and exploratory WEIRD versus less WEIRD culture comparisons. Cumulatively, variability in observed effect sizes was more attributable to the effect being studied than the sample or setting in which it was studied.

Although most people acknowledge the moral virtue in sacrificing oneself to save others, few actually endorse self-sacrifice. Seven experiments explored the cognitive and emotional mechanisms that underlie such endorsements. Participants responded to 1 of 2 moral dilemmas in which they could save 5 members of their country only by sacrificing themselves. Over 90% of participants acknowledged that the moral course of action was to sacrifice oneself to save others (Experiment 1), yet only those who were strongly fused with the group preferentially endorsed self-sacrifice (Experiments 2-7). The presence of a concern with saving group members rather than the absence of a concern with self-preservation motivated strongly fused participants to endorse sacrificing themselves for the group (Experiment 3). Analyses of think aloud protocols suggested that saving others was motivated by emotional engagement with the group among strongly fused participants but by utilitarian concerns among weakly fused participants (Experiment 4). Hurrying participants' responses increased self-sacrifice among strongly fused participants but decreased self-sacrifice among weakly fused participants (Experiment 5). Priming the personal self increased endorsement of self-sacrifice among strongly fused participants but further reduced endorsement of self-sacrifice among weakly fused participants (Experiment 6). Strongly fused participants ignored utilitarian considerations, but weakly fused persons endorsed self-sacrifice more when it would save more people (Experiment 7). Apparently, the emotional engagement with the group experienced by strongly fused persons overrides the desire for self-preservation and compels them to translate their moral beliefs into self-sacrificial behavior.

When people are ostrasized (i.e., rejected and excluded) by either an outgroup or an ingroup, they may either withdraw or engage in compensatory activities designed to reaffirm their social identity as a group member. The authors proposed here that individual differences in identity fusion (an index of familial orientation toward the group) would moderate the tendency for people to display such compensatory activity. Consistent with this reasoning, the results of four experiments showed that irrevocable ostracism increased endorsement of extreme, pro-group actions (fighting and dying for the ingroup) among fused persons but not among nonfused persons. This effect emerged when an outgroup ostracized fused individuals due either to their nationality (Experiment 1) or their personal preferences (Experiment 2). Similarly, ostracism by the ingroup amplified the tendency for fused persons to both endorse extreme pro-group actions, refuse to leave the group (Experiment 3), and donate money to an ingroup member (Experiment 4). Finally, compensatory activities emerged even when ostracism was based on being "too good" for the group, suggesting that a desire for self-enhancement does not mediate such activities (Experiment 4).

Just a decade ago, two psychologists, Swann, and Gómez, developed a new theoretical framework to explain extreme pro-group behaviors: identity fusion theory. Identity fusion refers to a visceral feeling of oneness with a group that motivates individuals to do extraordinary self-sacrifices on behalf of the group or each of its members. Since the formulation of the theory, interdisciplinary researchers of the five continents have conducted dozens of studies on identity fusion, both in laboratory and field settings. Research has deepened into the causes, consequences, underlying mechanisms, and applications of identity fusion. The development of fusion-based research has been steadfast and very prolific. Hence, the first section of the current manuscript includes an updated overview of this fast growing literature. This increasing interest for the theory has, however, been accompanied by a series of misconceptions and untested research assumptions, which we address in the second and third sections of the paper, concluding with a final section suggesting a future research agenda. Our aim is to help those interested in knowing more about identity fusion or about the causal mechanisms that lead individuals to risk their life and personal well-being for a group discarding common misconceptions as well as formulating more precise and nuanced hypotheses for future research.