“Gaydar” — the purported ability to infer whether people are gay or straight based on their appearance — seemed to get a scientific boost from a 2008 study that concluded people could accurately guess someone’s sexual orientation based on photographs of their faces.

In a new paper published in the Journal of Sex Research, researchers at the University of Wisconsin–Madison challenge what they call “the gaydar myth.” William Cox, an assistant scientist in the Department of Psychology and the lead author, says gaydar isn’t accurate and is actually a harmful form of stereotyping.

“Most people think of stereotyping as inappropriate,” Cox says. “But if you’re not calling it ‘stereotyping,’ if you’re giving it this other label and camouflaging it as ‘gaydar,’ it appears to be more socially and personally acceptable.”

Cox and his team questioned the validity of the previous research, citing differences in the quality of the photos used for the gay and straight people featured in the study. The gay men and lesbians, according to Cox’s studies, had higher quality pictures than their straight counterparts. When researchers controlled for differences in photo quality, participants were unable to tell who was gay and straight.

Another reason people’s judgments of sexual orientation are often wrong, Cox says, is that such a small percentage of the population — 5 percent or less — is gay.

“Imagine that 100 percent of gay men wear pink shirts all the time, and 10 percent of straight men wear pink shirts all the time. Even though all gay men wear pink shirts, there would still be twice as many straight men wearing pink shirts. So, even in this extreme example, people who rely on pink shirts as a stereotypic cue to assume men are gay will be wrong two-thirds of the time,” Cox says.

Cox authored the paper with professors Patricia Devine and Janet Hyde and UW–Madison graduate Alyssa Bischmann.

In one of the studies, Cox and his team manipulated what participants understood about gaydar by providing different explanations of gaydar for three groups. The researchers told one group that gaydar is real, told another that gaydar is stereotyping, and did not define gaydar for the third group.

The group that was led to believe gaydar is real stereotyped much more often than the other groups, assuming that men were gay based on the stereotypic cues — statements such as “he likes shopping.”

“If you tell people they have gaydar, it legitimizes the use of those stereotypes,” Cox says.

That’s harmful, he says, because stereotypes limit opportunities for members of stereotyped groups, narrowing how we think about them and promoting prejudice and discrimination — even aggression.

In a 2014 study on prejudice-based aggression, Cox and Devine had participants play a game with a subject in another room that involved administering electric shocks to the subject. When the research team implied that the subject was gay using a stereotypic cue, participants shocked him far more often than when the research team explicitly told them he was gay.

“There was a subset of people who were personally very prejudiced, but they didn’t want other people to think that they were prejudiced,” Cox says. “They tended to express prejudice only when they could get away with it.”

Cox hopes his research counteracts the gaydar myth and exposes it as something more harmful than most people realize.

“Recognizing when a stereotype is activated can help you overcome it and make sure that it doesn’t influence your actions,” Cox says.