For example, several years ago, I asked university students to indicate the degree to which they desired various characteristics in a relational partner (the type of relationship that they were asked to consider was manipulated) (Sprecher & Regan, 2002)
Although not generally referred to as studies on similarity, mate selection studies (in which participants are asked how much they desire various traits in a partner) have, in some cases, included items that refer to similarity. Included in the list, in addition to traits such as physical attractiveness, ambition, warmth and kindness, were four types of similarity: similarity on background characteristics (e.g., race, religion, social class), similarity on attitudes and values, similarity on social skills (e.g., interaction styles), and similarity on interests and leisure activities. Participants expressed preferences for all four types of similarity, as indicated by mean scores to the items that were above the midpoint of the response scales. The order in which the other types of similarity were rated in importance was: similarity in interests, similarity in social skills (interaction styles), and similarity in background characteristics. Although similarity was generally desired across all types of relationships, it was preferred to a greater degree in a marital partner, particularly as compared to in a friend.