One determinant of entitativity is a cognitive one—the perception of similarity. As we saw in our discussions of liking and loving, similarity is important across many dimensions, including beliefs, values, and traits. A group can only be a group to the extent that its members have something in common; at minimum, they are similar because they all belong to the group. If a collection of people are interested in the same things, share the same opinions and beliefs, or work together on the same task, then it seems they should be considered—by both themselves and others—to be a group. However, if there are a lot of differences among the individuals, particularly in their goals, values, beliefs, and behaviors, then they are less likely to be seen as a group.
Given the many differences that we have discussed in other chapters between members of individualistic and collectivistic cultures in terms of how they see their social worlds, it should come as no surprise that different types of similarity relate more strongly to perceptions of entitativity in each type of culture. For instance, similarity in terms of personal traits has been found to be more strongly associated with entiativity in American versus Japanese participants, with the opposite pattern found for similarity in terms of common goals and outcomes (Kurebayashi, Hoffman, Ryan, & Murayama, 2012).
People, then, generally get together to form groups precisely because they are similar. For example, perhaps they are all interested in playing poker, or follow the same soccer team, or like martial arts. And groups are more likely to fall apart when the group members become dissimilar and thus no longer have enough in common to keep them together (Crump, Hamilton, Sherman, Lickel, & Thakkar, 2010; Miles & Kivlighan, 2008).