1. GROUP 3

2. REFERENCE GROUP

4. In-group & Out-Group

6. IN-GROUP
OUT-GROUP

7. Associated phenomena In-group favoritism Outgroup derogation
This refers to the fact that under certain conditions people will prefer and have affinity for one’s in-group 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.
Outgroup derogation
Outgroup derogation is the phenomenon in which an outgroup is perceived as being threatening to the members of an in-group.
Social influence
People have been shown to be differentially influenced by in-group members. That is, under conditions where group categorization is psychologically salient people will shift their beliefs in line with in-group social norms.
Group polarization
his 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

8. Group homogeneity
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 in-group are perceived as being diverse, e.g. "they are alike; we are diverse”. This is especially likely to occur in regards to negative characteristics. Under certain conditions, in-group members can be perceived as being similar to one another in regards to positive characteristics. This effect is called in-group homogeneity.

9. Postulated role in human evolution
In evolutionary psychology, in-group 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 behavioral genetics suggests that biological mechanisms may exist which favor a coexistence of both flexible and essentialist systems.