Inequality in the minimal group paradigm: How relative wealth and its justification influence ingroup bias

This article details a registered report for a well-powered (N = 1500) experiment examining the influence of wealth inequality between groups on ingroup bias, as well as the potential moderating role of justification for the wealth distribution. Using the Minimal Group Paradigm, in which participants are assigned to groups with anonymous others and asked to allocate resources to ingroup or outgroup members, we randomly assigned participants to a relatively disadvantaged or a relatively advantaged group. Group assignments were ostensibly based on chance (weak justification), performance on a financial decision-making task (strong justification), or an ambiguous combination of the two (ambiguous justification). As expected, we found evidence for an inequity aversion hypothesis, with disadvantaged participants displaying heightened ingroup bias compared to their advantaged counterparts. Interestingly, however, our predictions regarding the moderating role of justification were not supported, with disadvantaged participants displaying the highest ingroup bias when the inequality was ambiguously justified. We discuss implications of these results for understanding the causal factors underlying ingroup bias.