“[The findings] are surprising in the sense that it’s the opposite bias that men tend to show in initial encounters, but we did expect that these biases would differ in established relationships,” she added. “It makes sense, since the goal in initial encounters might be to attract a partner, so over-perceiving their interest can help men feel more comfortable initiating a conversation or date. But the goal in relationships is to maintain the relationship.”

The research, which was conducted on mostly heterosexual couples, included three separate studies. In the first study, 44 couples completed surveys each night for three weeks. The surveys measured the participants’ sex drive as well as their daily feelings about their relationship.

In the second study, members of 84 couples were interviewed separately in a lab about their sex drive, how satisfied they were in their relationship and what they thought of their partner’s sex drive.

The third study involved 101 couples who completed a five- to 10-minute survey each day for three weeks in which they answered questions about their own sex drive and why they either felt motivated to pursue sex with their partner or not.

It turned out that men’s under-perception of their partner’s interest in sex was associated with their partner feeling more satisfied and committed to the relationship. Additionally, the researchers saw no consistent over- or under-perception bias in women.

“But, when women were higher in desire or on days when they were more motivated to avoid rejection, they demonstrated an under-perception bias as well,” Muise said. “This suggested to me that it is not just about gender but about who is higher in desire. Men tend to be higher in desire than women, on average, in relationships.”

The samples of same-sex couples in the study were too small to make a difference in the results, the researchers noted. “We conducted the analyses with and without the same-sex couples and the pattern of results remained the same,” they wrote in the study.

Andrea Meltzer, an assistant professor of psychology at Florida State University who was not involved in the research, said the findings were surprising and interesting.

“People’s behaviors are a function of their judgments and perception. That is, they tend to react to their partners based on their perception of their relationships,” she said. “For example, if they perceive their partners as satisfied, they tend to behave more positively. Thus, to have the most complete understanding of relationships, it is important to understand the source and function of intimate perceptions.”