A new study found that gay and bisexual men in Germany earn an average of €2.64 less per hour than straight men, even after wage differences were controlled for age, education, and industry.

Lesbian and bisexual women earned about €2 more per hour than straight women. Their wages were comparable to gay and bi men’s.

The study by the German Institute for Economic Research compared survey responses from 460 lesbians and gay men with results from 39,000 straight people.

Martin Kroh, the author of the study, said that the pay gap cannot be explained by differences in qualifications or education, but it might not necessarily be caused by pay discrimination.

“This is only an initial study. There are probably a whole set of explanations for the pay gap,” he said.

One possibility raised in the paper is minority stress. Kroh wrote that “stigmatization and discrimination, which can ultimately lead to chronic stress” might explain part of the pay gap in men’s wages.

Gay and bisexual men are also more likely to work overtime, which reduces their hourly wage in Germany.