Social Influence in Donation Behavior: The Effect of Mean, Variance, and Psychopathy

Charitable giving is a cornerstone of social welfare, and others’ donations can promote individual giving. However, the computational mechanisms through which social information shapes donation behavior, and how individuals differ in their responsiveness, remain poorly understood. Here, we investigated how the statistical properties of others’ donations shape individual giving, and how this was affected by individual differences in socio-affective traits. Across 4 pre-registered experiments (total N = 1,491), participants made donations before and after observing sequential donations from diverse others whose mean and variability were systematically manipulated. We found that observing generous average donations robustly increased individual giving, while observing stingy donations decreased it. Moreover, the variance in social information did not modulate this shift. In parallel, exposure to others’ donations consistently reduced the variability of individual donations, with stronger reductions when others’ donations were more consistent (versus more variable). Computational modeling revealed that a hybrid reinforcement learning model integrating initial donations with learned predictions of others’ donations captured participants’ donation behaviors well. At the individual level, changes in donations following social exposure were consistently positively associated with psychopathic traits. Model-derived parameters further revealed that people with higher psychopathic traits were more susceptible to social information, assigning greater weight to observed donations when making their second decisions. These results were replicated across all experiments, despite variations in donation magnitudes, population type, variability discrepancy, and incentive structures. Together, our findings demonstrate that the statistical structure of social information - its magnitude and variability - shapes the corresponding features of individual donations, and identify psychopathy as a key factor underlying heterogeneity in social influence.