Interindividual-Intergroup Discontinuity in the Prisoner’s Dilemma Game: How Common Fate, Proximity, and Similarity Affect Intergroup Competition

In two experiments with the PDG we manipulated the Campbell (1958), or Wertheimer (1923), indices of entitativity (common fate, proximity, and similarity) to examine when a set of individuals interacts with another set of individuals in the competitive manner that is characteristic of group-on-group interactions. Experiment 1 found that interactions between two 3-person sets were more competitive when participants within each set shared (versus did not share) common fate. In Experiment 2, the Wertheimer-Campbell indices were manipulated for one 3-person set only (targets). Participants in the other 3-person set were sequestered in separate rooms (observers). Observers as well as targets were more competitive when targets shared (versus did not share) common fate. Path analyses in both experiments supported the idea that common fate increases competition via increased own-set entitativity and subsequent greed, and via increased other-set entitativity and subsequent fear. We found no consistent evidence for the possible roles of proximity and similarity.