In developmental psychology, social identity theory has been used to explain conformity and socialization in peer groups (e.g., Archer, 1992 Harris, 1995 Leaper, 2000) and group-based prejudice (e.g., Bigler & Liben, 2007 Nesdale, 2004). Some key processes associated with important social identities include within-group assimilation (pressures to conform to the ingroup's norms) and forms of intergroup bias (positively evaluating one's ingroup relative to outgroup and possibly negatively evaluating the outgroup). Affiliation with a group confers self-esteem, which helps to sustain the social identity. Social identities are most influential when individuals consider membership in a particular group to be central to their self-concept and they feel strong emotional ties to the group. (As discussed earlier in the chapter, psychologists’ identification with a particular theoretical approach can also constitute a social identity.) Social identity theory addresses the ways that social identities affect people's attitudes and behaviors regarding their ingroup and the outgroup. Examples include sports teams, religions, nationalities, occupations, sexual orientation, ethnic groups, and gender. Social identity refers to the ways that people's self-concepts are based on their membership in social groups. Social identity theory was proposed in social psychology by Tajfel and his colleagues ( Tajfel, 1978 Tajfel & Turner, 1979).

Campbell Leaper, in Advances in Child Development and Behavior, 2011 5 Self-Categorization (and Social Identity) Theory

Assigning book identity