Many people hold fast to the idea that opposites attract, but in reality, couples are usually more similar than dissimilar. There’s a wealth of evidence suggesting that couples match on intelligence, attitudes, and physical attributes such as attractiveness and height.
Of course, humans aren’t averse to mixing it up. We shouldn’t be surprised to see couples who are different in personality or appearance. Sometimes these differences can lead to conflict—consider the septuagenarian couple from Florida whose recent argument about Donald Trump and Hillary Clinton escalated so quickly that emergency services were called. In other cases, couples are able to overlook such differences, or may be attracted to one another because of their differences.
However, couples don’t live in a vacuum. They live in a social environment populated by other people, all of whom have their own opinions about whether differences are appropriate or even legal. It wasn’t until the 1960s that the U.S. Supreme Court overturned the final anti-miscegenation laws, legalizing marriage between men and women of different races. But today, couples who visibly differ may still be subjected to discrimination and abuse. Sometimes our differences are racial, sometimes they're based on age—and sometimes couples differ visibly in their weight.
Mixed-weight Couples and Prejudice
Brian Collisson, a psychologist at Azusa Pacific University in California, decided to test the extent to which “mixed-weight” couples experience prejudice. Along with two colleagues from Ohio University and Marian University, Collisson ran a series of studies of weight difference and prejudice.
In the first study, 230 volunteers were told that they would be rating how favorable or unfavorable they felt toward a romantic couple that had participated in a previous experiment. The volunteers were told that the couple had not consented for their photographs to be shown to anyone else, but had selected a full-body avatar to represent themselves. A full-body avatar is an image of a human body, sometimes computer generated, that doesn’t possess any identifying characteristics. Like a shop mannequin sculpted to match a real person’s body shape.
Of course, the romantic couple was not genuine. In reality, Collisson simply presented volunteers with avatars that varied in weight. Sometimes the avatars were overweight, and sometimes a healthy weight. I should point out that “healthy weight” is the term used in the paper, and one that not everybody would agree with. Here it corresponds to a BMI of 18.5, while the "overweight" avatar corresponds to a BMI of 40. From now on, I’ll just refer to "higher BMI" and "lower BMI" avatars.
Half of the time, the volunteers saw avatars that matched in weight: Both had higher, or both lower, BMI. The other half of the time, the avatars differed in weight: Either the male or the female avatar had a higher BMI, while the partner had a lower BMI.
Volunteers rated how positively they felt about each couple using a 100 point scale from cold/unfavorable to warm/favorable.
As you might have expected, couples in which both members had a low BMI received the highest favorability ratings: 64 out of 100. Couples in which both partners had a high BMI received somewhat lower ratings: 58 out of 100. But the lowest ratings of all were reserved for mixed-weight couples: around 51 out of 100. It’s worth noting that it didn’t seem to matter if it was the male or female partner who had the higher BMI. In both cases, the favorability scores were about the same.
Weighing Your Options
For their next experiment, Collisson and his colleagues asked a new group of volunteers to help refine the algorithm for a new dating website. The volunteers read a description of a dating website user. This description included information about the user’s weight. The volunteer’s task was then to create an ideal partner for this user, selecting the type of characteristics they thought most suitable. Of course, one of these characteristics was body size.
After they had made their choices, the volunteers were shown avatars of the couples they had matched. As before, sometimes these couples were matched in weight and sometimes they had different weights. The volunteers now rated on a 8-point scale how happy they were with each match.
The results of the experiment showed that matchmakers had chosen heavier partners for heavier users. When the user had a lower BMI, the volunteers chose, on average, a partner with a BMI of 22; when the user had a higher BMI, the volunteers chose partners with BMIs around 32.
And were the volunteers happy with their matches? When volunteers were shown avatars of their matched couples, they rated couples with similar weights at around 6 out of 8, regardless of whether both partners were heavier or lighter. But when one partner had a high BMI and the other a low BMI, scores were much lower—around 3 out of 8. Matchmakers much preferred couples to be similar in weight, and thought they had made a bad match when partners were dissimilar in weight.
Advice for Mixed-Weight Couples
In a third study, the researchers tested whether mixed-weight couples receive different dating advice than similar-weight couples. They found that volunteers were more likely to suggest that similar-weight couples take more active dates (e.g. taking a bike ride together) and more public dates (e.g. taking in a concert together). Matched-weight couples were also advised to spend more on their dates, and to introduce their dates to their close friends and family earlier in their relationship. In other words, couples that didn’t match on weight were advised to date in secret and to take their relationships less seriously.
Why the Hate for the Mixed-weight?
In their final experiment, the researchers sought to find out why we seem to hate on mixed-weight couples. They had a new group of volunteers complete a battery of surveys as a means of testing multiple competing theories.
One possibility is that people are simply prejudiced against couples whose members are different from each other. It may not matter that the couple is mixed-weight: The difference could be in race, socioeconomic class, age, or any other trait. Another possibility is that people don’t like it when one partner seems to be getting a bad deal: Weight is related to attractiveness, and perhaps we don’t think it is "fair" if one person is attached to a partner who is "out of their league." A third possibility is that people simply prefer the status quo, and are unhappy when it is challenged: It feels safer to stand behind established social and political systems than to experiment with new possibilities, and couples who match on weight may seem more “conventional.”
The results suggest that the first possibility was the best explanation: We are prejudiced against couples who are different because they are different. The other theories explained the volunteers' behavior to some extent, but it appeared that a general dislike of mixed-status couples was the main driver of prejudice.
Collisson and his colleagues wrote:
"It is possible that people’s prejudices and discriminatory behavior may contribute to mixed-weight couples’ conflict and potential relationship dissolution. Future research that assesses the effect of stigmatization on the long-term physical and mental health of mixed-weight couples is an important extension of the current research."
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Collisson, B., Howell, J. L., Rusbasan, D., & Rosenfeld, E. (in press). “Date someone your own size”: Prejudice and discrimination toward mixed-weight relationships. Journal of Social and Personal Relationships. View summary