Social psychologists have long recognized that in a variety of settings, people behave differently in groups than they would by themselves. At times, people perform more effectively and make better decisions when part of a group. Often, however, being part of a group results in reduced performance, poorer decisions, and sometimes-tragic consequences (see Janis, 1972, for examples). That groups often place great pressure on individuals to exhibit specific behaviors is particularly evident in gangs, where the consequences of defying group authority can be brutal. In other cases, group influence is subtle, and an individual may change his or her behavior because the situation is ambiguous and because the influence of others leads to alternate action (or even inaction when a response is ...