Group-produced enhancement of members' preexisting tendencies; a strengthening of the members' average tendency, not a split within the group.
groupthink
"The mode of thinking that persons engage in when concurrence-seeking becomes so dominant in a cohesive ingroup that it tends to override realistic appraisal of alternative courses of action" (Irving Janis [1971]).
social comparison
Evaluating one's opinions and abilities by comparing oneself to others.
