Tajfel (1972) introduced the concept of “social identity,” which refers to a person’s knowledge that he or she belongs to certain social groups and which involves emotional and value significance because of that group membership. A social group is defined as more than two people who (1) identify and evaluate themselves in the same way, (2) have the same definition of who they are and what attributes they have, and (3) follow the same patterns for how they interact with others who are not in their group (Hogg, 2006). Group membership refers to a collective sense of “us” versus “them,” and self-identification refers to an individual sense of “me” versus “you.”

Social identity refers to those aspects of an individual’s self-image that derive from the social categories to which they perceive themselves as belonging (Tajfel & Turner, 1986). The theory is based on some general assumptions: (1) people strive to maintain and improve their self-esteem and a positive self-concept; (2) social group, or category, membership can enhance or lower someone’s self-esteem and self-concept; and (3) people evaluate the positive or negative attributes of groups to which they belong compared to those of other groups to which they do not belong, such as for status and prestige.