Psychological concept or theory on majority and minority

Hello I'm studying the consumer psychology. I want to know which theory or concept can be used to explain this scenario. There are two types of communities based on residents' ethnicity distributions. If there is no ethnicity percentage more than 50%, we define it as one ethnicity-mixed community; if there is at least one ethnicity more than 50%, we assign the ethnicity with the highest percentage as the dominant ethnicity for this ethnicity-homogeneous community. For the ethnicity-homogeneous communities, there are another two cases: the resident has the same ethnicity as the dominant community ethnicity; that is, this resident is the majority in this community. The resident has the different ethnicity from the dominant community ethnicity; that is, the resident is the minority in this ethnically homogeneous community. We find that people from an ethnically homogeneous community, no matter whether they are in ethnicity majority or minority, they tend to return fewer purchased items than those from ethnicity-mixed communities. Can you recommend some psychological theories or concepts for this scenario? Thanks for your help.