Tajfel, H. (1970). Experiments in intergroup discrimination. Scientific American, 223, 96-102.
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Tajfel (1970) examined whether particpants would discriminate against outgroup members when their group was defined by minimal information. Participants (adolescent boys) completed a computer task and were given a list of participants who scored similarly to them on the same task. The list did not indicate any personal identifiers (e.g., sex, race, age) other than a participant identification number. Participants were then given another list of participant identification numbers and were told that those people scored similarly on the same task (but differently from the participant). When participants were asked to allocate money to the different participants on both lists, participants gave more money to individuals who scored similarly to themselves compared to individuals who scored differently. In the control condition where participants were not told any information about score similarity, participants allocated money more equitably.
Tajfel demonstrated that a "minimal group" is all that is necessary for individuals to exhibit discrimination against an outgroup. This experiment is considered a classic in psychology because it demonstrates that intergroup conflict is not required for discrimination to occur.