In-group bias in prisons

We conducted a field experiment in a typical Chinese prison to examine the in-group bias of groups with a stigmatized identity. Inmates were given the opportunity to work for a charity. We found evidence of both pro-sociality and in-group favoritism among inmates. In particular, inmates increased their efforts when their output contributed to a charity and worked even harder when the beneficiary of their efforts have a prisoner identity. However, inmates who have been in prisons for a longer period put in relatively less effort in helping a beneficiary who is a prisoner. This negative correlation was not observed when the beneficiary was an outsider. These findings highlight the importance of social interaction in the formation of in-group bias.