Ingroup cooperation among Japanese baseball fans using the one-shot prisoner's dilemma game

This study aimed to examine the external validity of social identity theory (SIT) and the bounded generalised reciprocity hypothesis (BGR) to generate ingroup cooperation in real groups. Previous research has demonstrated the existence of ingroup cooperation predicted by both theories in the minimal group, whereas neither theory was supported in real groups. However, ingroup cooperation predicted by both theories was revealed among Japanese baseball fans after controlling for confounding factors. Furthermore, previous research showed that ingroup cooperation was better explained by the BGR than by the SIT when the cost of cooperation was high. The limitation of these studies is that ingroup cooperation was measured in terms of behavioural intention (a vignette experiment). This study employed a one-shot prisoner's dilemma game to measure ingroup cooperation among Japanese baseball fans. The results supported only BGR in that ingroup cooperation was enhanced in situations wherein participants could expect a reciprocal relationship with their game partner.