who has given the concepts of ingroup and outgroup
Ingroups and outgroups 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.[1][2][3][4][5]
Ringelmann effect The Ringelmann effect is the tendency for individual members of a group to become increasingly less productive as the size of their group increases.[1] This effect, discovered by French agricultural engineer Maximilien Ringelmann (1861–1931), illustrates the inverse relationship that exists between the size of a group and the magnitude of group members’ individual contribution to the completion of a task. While studying the relationship between process loss (i.e., reductions in performance effectiveness or efficiency) and group productivity, Ringelmann (1913) found that having group members work together on a task (e.g., pulling a rope) actually results in significantly less effort than when individual members are acting alone. Furthermore, Ringelmann discovered that as more and more people are added to a group, the group often becomes increasingly inefficient, ultimately violating the notion that group effort and team participation reliably leads to increased effort on behalf of the members.[1][2]