Do opposites attract or do birds of a feather flock together?

Do people tend to select romantic partners that are similar to them or opposite to them? And does spouse similarity lead to marital happiness? In one of the most comprehensive studies ever undertaken on these questions, researchers at the University of Iowa find that people tend to marry those who are similar in attitudes, religion and values. However, it is similarity in personality that appears to be more important in having a happy marriage. The findings appear in the February issue of the Journal of Personality and Social Psychology, published by the American Psychological Association (APA).

Psychologist Eva C. Klohnen, Ph.D., and graduate student Shanhong Luo, M.A., of the University of Iowa looked at assortative mating issues (mating based on similar or opposite characteristics) among 291 newlyweds who had participated in the Iowa Marital Assessment Project. The newlyweds had been married less than a year at the time the study began and had dated each other for an average of three and a half years. The couples were assessed on a broad range of personality characteristics, attitudes and relationship quality indicators.

Results show that couples were highly similar on attitudes and values; however, they had little or no above-chance similarity on personality-related domains such as attachment, extraversion, conscientiousness and positive or negative emotions. There is no evidence that opposites attract. What is most intriguing is that when the researchers assessed marital quality and happiness, they found that personality similarity was related to marital satisfaction, but attitude similarity was not.

“People may be attracted to those who have similar attitudes, values, and beliefs and even marry them – at least in part – on the basis of this similarity because attitudes are highly visible and salient characteristics and they are fundamental to the way people lead their lives,” explain the authors. Personality-related characteristics, on the other hand, take much longer to be known and to be accurately perceived and are not likely to play a more substantial role until later in the relationship, they add.

“However, once people are in a committed relationship, it is primarily personality similarity that influences marital happiness because being in a committed relationship entails regular interaction and requires extensive coordination in dealing with tasks, issues and problems of daily living. Whereas personality similarity is likely to facilitate this process, personality differences may result in more friction and conflict in daily life,” say the authors. “As far as attitudes are concerned, people who chose to marry each other should be well aware of how similar or different they are on these domains because attitudes are very visible and salient. This suggests that attitudinal and value differences, when they exist, are part of a conscious decision to stay together on the basis of other important considerations, according to Luo and Klohnen.

Given that their research indicates that similarity in attitudes and values may play a different role in relationship development than does personality similarity, Luo and Klohnen suggest that future research should examine how similarity in different domains are related to relationship outcomes for couples in earlier and later stages of relationship development.