Behavior that occurs when two or more people interact is the subject of the study of behavior in groups.
The presence of others may promote a variety of behavioral processes.
The phenomenon of social facilitation, improved performance due to the presence of others, is believed to be due to a fear of evaluation as well as others' presence.
Social interference (also referred to as social loafing) is decreased performance when working in a group. Robert Zajonc found that social facilitation occurs more frequently if a task is simple or well learned and social interference when a task is complex or unpracticed.
Group polarization is a process whereby an individual's preexisting attitudes are strengthened as a consequence of group discussion that supports those attitudes. One explanation of the phenomenon is that in a group individual responsibility becomes diffused because an individual cannot be held responsible for the group's decisions.
Groupthink is the phenomenon of group members supporting one another and seeking agreement and group cohesiveness rather than realistically appraising alternatives. Because the practice discourages disagreement, unpopular but important information may be ignored in such a group's decision making.