A new study claims gaydar isn’t real—and actually reinforces negative stereotypes.

"Most people think of stereotyping as inappropriate,” says researcher William Cox of the University of Wisconsin-Madison. "But if you're not calling it 'stereotyping'—if you're camouflaging it as 'gaydar'—it appears to be more socially and personally acceptable.”

A 2008 study previously concluded people could accurately guess someone's sexual orientation based on photographs. But Cox’s teams says that study was flawed because it used different quality photos for straight and gay subjects, biasing people’s choices.

When all photos were the same quality, interviewees were unable to determine sexual orientation.

Cox also says since gays and lesbians are such a small percentage of the total population, people often make false assumptions.

"Imagine that 100% of gay men wear pink shirts all the time, and 10% 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.”

And people who rely on pink shirts as a cue to tell them if someone's gay would be wrong two-thirds of the time.

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

In their studies, Cox and his team manipulated what participants understood about gaydar—telling one set that gaydar was scientifically verified, another that it was just stereotyping, and not telling a third group anything.

The group that was told gaydar was legitimate was quicker to label male candidates gay, making statements like "he likes shopping."

"If you tell people they have gaydar,” says Cox, "it legitimizes stereotypes."

Last year, Cox had participants play a game that required them to shock a man in a different room. He found they shocked the man far more often when they were told he was gay.

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