Social influence protects collective decision making from equality bias

A basic tenet of research on wisdom of the crowds-and key assumption of Condercet's (1785) Jury Theorem-is the independence of voters' opinions before votes are aggregated. However, we often look for others' opinions before casting our vote. Such social influence can push groups toward herding, leading to "madness of the crowds." To investigate the role of social influence in joint decision making, in Experiment 1 we had dyads of participants perform a visual oddball search task together. In the Independent (IND) condition participants initially made a private decision. If they disagreed, discussion and collective decision ensued. In the Influence (INF) condition no private decisions were made and collective decision was immediately negotiated. Dyads that did not accrue collective benefit under the IND condition improved with added social influence under the INF condition. In Experiment 2, covertly, we added noise to 1 of the dyad members' visual search display. The resulting increased heterogeneity in dyad members' performances impaired the dyadic performance under the IND condition (Bahrami et al., 2010). Importantly, dyadic performance improved with social influence under the INF condition, replicating results in Experiment 1. Further analyses revealed that under the IND condition, dyads exercised equality bias (Mahmoodi et al., 2015) by granting undue credit to the less-reliable partner. Under the INF condition, however, the more-reliable partner (correctly) dominated the joint decisions. Although social influence may impede collective success under ideal conditions, our results demonstrate how it can help the group members overcome factors such as equality bias, which could potentially lead to catastrophic failure.