In sociology and social psychology, an ingroup is a social group to which a person psychologically identifies as being a member. By contrast, an outgroup is a social group with which an individual does not identify. For example, people may find it psychologically meaningful to view themselves according to their race, culture, gender, age, or religion. It has been found that the psychological membership of social groups and categories is associated with a wide variety of phenomena.
The terminology was made popular by Henri Tajfel and colleagues during his work in formulating social identity theory. The significance of ingroup and outgroup categorization was identified using a method called the minimal group paradigm. Tajfel and colleagues found that people can form self-preferencing ingroups within a matter of minutes and that such groups can form even on the basis of seemingly trivial characteristics, such as preferences for certain paintings.
The psychological categorization of people into ingroup and outgroup members is associated with a variety of phenomena. The following examples have all received a great deal of academic attention.
This refers to the fact that under certain conditions, people will prefer and have affinity for one's ingroup over the outgroup, or anyone viewed as outside the ingroup. This can be expressed in one's evaluation of others, linking, allocation of resources, and many other ways.
Discrimination between ingroups and outgroups is a matter of favoritism towards an ingroup and the absence of equivalent favoritism towards an outgroup. Outgroup derogation is the phenomenon in which an outgroup is perceived as being threatening to the members of an ingroup. This phenomenon often accompanies ingroup favoritism, as it requires one to have an affinity towards their ingroup. Some research suggests that outgroup derogation occurs when an outgroup is perceived as blocking or hindering the goals of an ingroup. It has also been argued that outgroup derogation is a natural consequence of the categorization process.
People have been shown to be differentially influenced by ingroup members. That is, under conditions where group categorization is psychologically salient, people will shift their beliefs in line with ingroup social norms.
This generally refers to the tendency of groups to make decisions that are more extreme than the initial inclination of its members, although polarization toward the most central beliefs has also been observed. It has been shown that this effect is related to a psychologically salient ingroup and outgroup categorization.
Categorization of people into social groups increases the perception that group members are similar to one another. An outcome of this is the outgroup homogeneity effect. This refers to the perception of members of an outgroup as being homogenous, while members of one's ingroup are perceived as being diverse, e.g. "they are alike; we are diverse". This is especially likely to occur in regard to negative characteristics. Under certain conditions, ingroup members can be perceived as being similar to one another in regard to positive characteristics. This effect is called ingroup homogeneity.
In evolutionary psychology, ingroup favoritism is seen as an evolved mechanism selected for the advantages of coalition affiliation. It has been argued that characteristics such as gender and ethnicity are inflexible or even essential features of such systems. However, there is evidence that elements of favoritism are flexible in that they can be erased by changes in social categorization. One study in the field of behavioural genetics suggests that biological mechanisms may exist which favor a coexistence of both flexible and essentialist systems.