PULLMAN, Wash.--Washington State University researchers have established a categorical distinction between people who are heterosexual and those who are not. By analyzing the reported sexual behavior, identity and attraction of more than 33,000 American adults, they found that 3 percent of men and 2.7 percent of women are not heterosexual. They also found notable issues on several mental health fronts.

The findings are a clear departure from the homosexual-heterosexual continuum used to describe sexual orientation since it was hypothesized by sexologist Alfred Kinsey in 1948. However, the findings do support more recent biological hypotheses of sexual orientation.

"There are distinct qualitative differences in sexual orientation, which means that there are distinct categories of people based on sexual orientation," said Alyssa Norris, a WSU doctoral candidate and lead author of the study, published in the journal Psychological Science.

Norris and her colleagues also identified several alarming mental health issues among non-heterosexuals. Nearly three out of ten non-heterosexual men--roughly twice that of heterosexual men--met the diagnostic criteria for depression. Non-heterosexual women were much more likely to abuse or depend on alcohol. Non-heterosexual men and women were more likely to meet the criteria for anxiety and other mood disorders and to think about suicide.

The researchers said the social stigmatization of gays, lesbians and other non-heterosexuals could be a factor in their mental health.

"By actually getting some understanding of how to categorize people and the unique challenges they face, we're getting a lot more insight into their well-being and their experiences," said Norris.

Norris, WSU psychology department chair David Marcus, and Bradley Green of the University of Southern Mississippi used data from the National Epidemiologic Survey on Alcohol and Related Conditions, which conducted personal interviews with more than 35,000 randomly selected adults. The survey asked respondents about which genders they've had sex with, getting at the behavior studied by Kinsey, as well as their sexual identity and who they're most attracted to. Attraction, said Norris, has only recently been regularly studied, although one could argue it is most central to one's sexual orientation.

Norris, Marcus, and Green used a set of statistical methods called taxometrics, which was developed specifically to determine if people are distributed on a spectrum or if they are part of meaningful groups, or taxons.

"People at some point are crossing a threshold between one group and another group," said Marcus. "Why they do it, we can't answer in this study. But that they do it tells researchers they should be looking at that question, not as much at the continuum question. The most radical, extreme version of that would be to say Kinsey led a lot of this research down the wrong path as much as he was a pioneer whose work helped destigmatize same-sex relationship and inclinations."

The researchers' findings have numerous implications.

Foremost, they say, is the ability to home in on the mental health impact of cultural issues non-heterosexuals are more likely to face. The findings are also consistent with those of biologists who examine how genes and hormones shape sexual orientation.

Another implication of the findings is they leave little room for calling homosexuality a lifestyle choice.

"A lifestyle does not fit into a taxon," said Marcus. "People who use the language of 'choice' and 'lifestyle' are negating 'born that way' or any of the terminology that would assume that these are genuine differences that are legitimate."

Marcus said the findings also go against the notion of "conversion therapy," which ostensibly would move a person along a continuum towards heterosexuality.

"Conversion therapy is fundamentally changing who they are," he said. "Generally we can't do that in psychology."'

Rather, the taxometric results establish a group of people that are, in effect, bona fide heterosexuals. Then there's another group that is not a continuum but an assemblage, a variety of people united in their same-sex sexual orientation but who may reflect diverse sexual identities.

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