The Common In-group Identity Model (CIIM) has roots in Intergroup Contact Theory (ICT).
Intergroup Contact Theory explains processes involved in reducing prejudice between groups when individuals from those groups interact. Thus, we assume people who are part of different groups (i.e., in-groups) are likely to have prejudices about each other, since ICT predicts contact between those people might reduce the prejudice. This is where CIIM comes in-it provides another perspective of how prejudice between people of different groups can be reduced.
Samuel Gaertner and John Dovidio created the CIIM, which predicts if two different in-groups, respectively made up of individuals who have prejudice towards those in the other group, are combined into one, ‘superordinate’, in-group, then the individuals will cognitively perceive the former ‘out-group’ members as part of the new and larger ‘in-group’, and prejudice between the former rivals will be reduced because they would now perceive themselves as part of the same in-group. Another way to say this is that they will have cognitively ‘recategorized’ former out-group members as part of the new and larger in-group.
Consider the 2000 film Remember the Titans, based on a true story; white and black players who have prejudice towards each other are placed in a new superordinate group (an American high school football team), and eventually the prejudice is successfully reduced. Another film based on a similar true story that serves as an example of CIIM is Invictus (2009), based on the 1995 Rugby World Cup in South Africa and Nelson Mandela’s efforts to support the racially mixed South African team shortly after the end of apartheid.
Consider yet another example–a study found White people evaluated Black people more favorably when they interacted with them as members of the same in-group than as separate individuals (Nier et al., 2001).