My friends are all alike — the relation between liking and perceived similarity in person perception

Highlight
• People have more knowledge about liked others compared to disliked others.
• Positivity displays a smaller diversity than negativity.
• People perceive liked others as more similar to one another than disliked others.
• Thinking about people's positive traits makes them appear more similar to one another.

Past research showed that people accumulate more knowledge about other people and objects they like compared to those they dislike. More knowledge is commonly assumed to lead to more differentiated mental representations; therefore, people should perceive others they like as less similar to one another than others they dislike. We predict the opposite outcome based on the density hypothesis (Unkelbach, Fiedler, Bayer, Stegmüller, & Danner, 2008); accordingly, positive impressions are less diverse than negative impressions as there are only a few ways to be liked but many ways to be disliked. Therefore, people should perceive liked others as more similar to one another than disliked others even though they have more knowledge about liked others. Seven experiments confirm this counterintuitive prediction and show a strong association between liking and perceived similarity in person perception. We discuss the implications of these results for different aspects of person perception.