How many bad apples does it take to spoil the whole barrel? Social exclusion and toleration for bad apples

In social dilemmas, where personal welfare is in conflict with collective welfare, there are inherent incentives to act non-cooperatively. Moreover, there is evidence that the example of a few uncooperative group members ("bad apples") is more influential than the example of comparable numbers of cooperative members (a bad apple effect). Two studies are reported that examine the functional relationship between the number of likely bad apples and individual cooperation, and whether and when the threat of social exclusion for uncooperative behavior may effectively counter the temptation to follow the example of such "bad apples". It is shown that (a) the threat of exclusion is sufficient to counter the temptation to follow a few bad apples' example, (b) such threats cannot, however, overcome the cooperation-degrading effects of large numbers (e.g., a majority) of bad apples, and (c) the effectiveness of such threats may be greater in relatively smaller groups. © 2009 Elsevier Inc. All rights reserved.