The Effect of Ingroup vs. Outgroup Memb...

Providing potential donors with information about the behavior of others (i.e., socialinformation) is an increasingly used strategy to nudge prosocial decision-making. Inthe present study, we investigated the effect of ingroup vs. outgroup information onparticipants’ charity preferences by applying a Drift Diffusion Model (DDM) approach. In ajoint evaluation scenario, we manipulated different levels of ingroup/outgroup preferenceratios for two charities within subjects. Every subject was presented with three stimulustypes (i.e., high, medium, and low ingroup ratio) randomized in 294 trials divided intosix blocks. We expected that for stimuli with a high ingroup/outgroup ratio, participantsshould more often and faster decide for the ingroup’s most favored charity. We expectedthat the speed of evidence accumulation will be higher the larger the ingroup/outgroupratio. Additionally, we investigated whether variations in model parameters can explainindividual differences in participants’ behaviors. Our results showed that people generallyfollowed ingroup members’ preferences when deciding for a charity. However, on findingan unexpected pattern in our results, we conducted post-hoc analyses which revealedtwo different behavioral strategies used by participants. Based on participants’ decisions,we classified them into “equality driven” individuals who preferred stimuli with the leastdifference between ingroup and outgroup percentages or “ingroup driven” individualswho favored stimuli with the highest ingroup/outgroup ratio. Results are discussed in linewith relevant literature, and implications for practitioners are given.