In sociology and social psychology, in-groups and out-groups are social groups to which an individual feels as though he or she belongs as a member, or towards which they feel contempt, opposition, or a desire to compete, respectively. People tend to hold positive attitudes towards members of their own groups, a phenomenon known as in-group bias. The term originates from social identity theory which grew out of the work of social psychologists Henri Tajfel and John Turner .
In-group favoritism refers to a preference and affinity for one's in-group over the out-group or anyone viewed as outside the in-group. This can be expressed in evaluation of others, linking, allocation of resources, and many other ways. A key notion in understanding in-group/out-group biases is determining the psychological mechanism that drives the bias. One of the key determinants of group biases is the need to improve self-esteem. That is individuals will find a reason, no matter how insignificant, to prove to themselves why their group is superior.
Intergroup aggression is any behavior intended to harm another person because he or she is a member of an out group. Intergroup aggression is a by product of in-group bias, in that if the beliefs of the in-group are challenged or if the in-group feels threatened, then they will express aggression toward the out-group. The major motive for intergroup aggression is the perception of a conflict of interest between in-group and out-group. The way the aggression is justified is through dehumanizing the out-group, because the more the out-group is dehumanized the "less they deserve the humane treatment enjoined by universal norms. "
The out-group homogeneity effect is one's perception of out-group members as more similar to one another than are in-group members, e.g. "they are alike; we are diverse. " The out-group homogeneity effect has been found using a wide variety of different social groups, from political and racial groups to age and gender groups. Perceivers tend to have impressions about the diversity or variability of group members around those central tendencies or typical attributes of those group members. Thus, out-group stereotypicality judgments are overestimated, supporting the view that out-group stereotypes are over-generalizations In an experiment testing out-group homogeneity, researchers revealed that people of other races are perceived to look more alike than members of one's own race. When white students were shown faces of a few white and a few black individuals, they later more accurately recognized white faces they had seen and often falsely recognized black faces not seen before. The opposite results were found when subjects consisted of black individuals.
Prejudice is a hostile or negative attitude toward people in a distinct group, based solely on their membership within that group. There are three components. The first is the affective component, representing both the type of emotion linked with the attitude and the severity of the attitude. The second is a cognitive component, involving beliefs and thoughts that make up the attitude. The third is a behavioral component, relating to one's actions – people do not just hold attitudes, they act on them as well. Prejudice primarily refers to a negative attitude about others, although one can also have a positive prejudice in favor of something. Prejudice is similar to stereotype in that a stereotype is a generalization about a group of people in which identical characteristics are assigned to virtually all members of the group, regardless of actual variation among the members.