It is not surprising that we tend to like people who are similar to us, and there is a large body of research that confirms this. But the reasons why we like people who are like us can be complex. First, there is a difference between actually having a lot in common with someone (called actual similarity) and believing that we have a lot in common (perceived similarity). These two kinds of similarity are certainly related, but they're not exactly the same thing. You may think you have a lot in common with someone, but you might be mistaken. Or you might initially assume you'll have a lot in common with a person you don't know that much about, only to find out that you're not really on the same wavelength once you get to know each other. Or you may assume you have a lot in common with someone because you like them. There are also many different reasons why we might like people who are similar to us. Perhaps we anticipate that someone who has a lot in common with us will like us more. Or maybe we just find it more fun to hang out with someone who shares our interests.
The less information we have about a person, the more actual similarity affects liking. In studies where people just read about a stranger and don't actually meet them, finding out they have a lot in common with the stranger greatly boosts liking, because they have nothing else upon which to base their impression. In studies where people actually met strangers with whom they had more or less in common, actual similarity affected liking, but not as much as in studies where people never met the stranger. In longer-term situations where people have more of a chance to really know each other, like friendships and romantic relationships, actual similarity has no effect — only perceived similarity does. In part, this is because in long-term relationships people have already filtered out dissimilar people they don't like. (You won't be friends with or date someone you dislike due to having nothing in common.) In all of these types of studies, perceived similarity had a large effect on liking. So it's more important to think you have a lot in common with someone than it is to actually have a lot in common.
Researchers have proposed several different reasons why similarity might increase liking. These reasons were examined in a study by Adam Hampton, Amanda Fisher Boyd, and Susan Sprecher, just published in the Journal of Social and Personal Relationships:
- Consensual validation: Meeting people who share our attitudes makes us feel more confident in our own attitudes about the world. If you love jazz music, meeting a fellow jazz-lover shows you that loving jazz is OK, and maybe even a virtue.
- Cognitive evaluation: This explanation focuses on how we form impressions of other people by generalizing from the information we have. So we learn that a person has something in common with us, and that makes us feel positively about that person, because we feel positively about ourselves. We then assume that the other person, like us, has other positive characteristics.
- Certainty of being liked: We assume that someone who has a lot in common with us is more likely to like us. And in turn, we are more likely to like people if we think they like us.
- Fun and enjoyable interactions: It's just more fun to hang out with someone when you have a lot in common.
- Self-expansion opportunity: According to self-expansion theory, one benefit of relationships is that we can gain new knowledge and experiences by spending time with someone else. Even though a dissimilar person would be more likely to actually provide new knowledge and experiences, research has shown that people are more likely to see self-expansion opportunities when interacting with someone who is similar, rather than dissimilar, to them.
In their study, Hampton and colleagues examined how well each of these five reasons could explain links between similarity and liking in situations involving both actual and perceived similarity.
In this study, 174 undergraduate students interacted with each other in pairs. Before meeting, the students didn't know anything about each other. The students then completed a questionnaire about their likes and interests (e.g., "Reality show or sitcom?") and their personality (e.g., "Sloppy or neat freak?"). The researchers gave them a bogus version of that same questionnaire supposedly completed by their interaction partner. The answers were rigged to be either highly similar or dissimilar to the participant's own answers.
After viewing the bogus information, participants rated how similar they thought the person was to them (perceived similarity) and rated how much they liked that person, based on the information in the questionnaire. Then the two participants had the chance to meet and get acquainted. Once they actually got to know each other, they again rated perceived similarity and liking.
Key to this study, both before and after interacting with each other, the participants answered several questions designed to measure the five different reasons for liking. (The questions were phrased differently when referring to the future interaction versus the past interaction.)
- Consensual validation: "My future interaction partner will probably support my attitudes and ideas," and "My future interaction partner will likely be 'validating' — that is, they will help to convince me that I am correct in how I approach life."
- Cognitive evaluation: For example, "My future interaction partner is probably well-respected."
- Certainty of being liked: For example, "I think my future interaction partner will like me."
- Fun and enjoyment: For example, "My future partner and I will probably laugh during our interaction period."
- Self-expansion opportunity: For example, "Interacting with my future partner would likely open the door to new experiences."
First, they found that people generally liked their interaction partner more, both before and after the interaction, if they were led to believe their partner was similar to them. However, the effects of perceived similarity were stronger than the effects of the experimental manipulation of the bogus information, with the bogus information actually having no effect on liking after the interaction. This makes sense, because any assumption of similarity based on the false information had no connection to the reality of actually interacting with that person. Thus, the perceptions of similarity based on the real interaction wiped out any effects of the bogus similarity information.
Consensual validation helped to explain why people who perceived greater similarity liked their partners more after the interaction, but not before. Presumably feeling validated requires more of a chance to connect with someone who shares your values and preferences, rather than just a vague notion that you may have some things in common. Certainty of being liked by the partner helped to explain why people liked similar partners more, both before and after the interaction. Expecting to enjoy the interaction also helped to explain why people liked similar partners more before the interaction, and actual enjoyment of the interaction also explained why people like similar partners more after they interacted. The results also suggested that these feelings of enjoyment were by far the strongest factor and overrode the effects of consensual validation and certainty of being liked. The researchers point out that this might be especially true among a sample of young college students and that for older adults, other factors may better explain why similarity leads to liking.
It is also important to remember that these pairs of strangers already had a reasonable amount in common, since they were both students at the same school and approximately the same age. Other factors, besides enjoyment of the interaction, might explain the similarity-liking connection more in contexts where people are not always interacting with those who are demographically similar. If people had interacted with others of a different age or social class, then for those who interacted with someone who was similar on those dimensions, certainty of being liked may have played a larger role if they were concerned that someone from a different social group might not accept them.
This study helps us to understand why similarity can foster liking when people first meet. But it doesn't shed much light on why perceived similarity is important in longer-term relationships. It is likely that in long-term relationships, factors beyond fun and enjoyment contribute to the positive effects of similarity. For example, romantic partners who are similar to each other have fewer conflicts, and married couples with similar educational attainment and age are less likely to divorce.