Some things are spectrums: rainbows, radiation, political positions. But as much as we’ve grown accustomed to the idea, sexual orientation might not be one of them.

A new study from researchers at Washington State University (WSU) analyzed data from a survey of over 33,000 U.S. adults and found that a “taxonic,” or categorical, model was better suited for describing sexual orientation than a continuum model like the famous Kinsey scale. In other words, sexuality isn’t a sliding scale so much as it is a complicated multiple choice question.

“These results demonstrate that sexual orientation is not a matter of degree but rather of distinct and meaningful categories,” their study, now published in the journal Psychological Science, concludes.

In an interview with The Daily Beast, Alyssa Norris, a WSU doctoral candidate and the study’s lead author, acknowledged the popularity of the notion that sexuality is a spectrum but maintained that the data simply doesn’t back it up.

“I believe that people want to respect and value individual differences in this area, and recognizing sexuality as fluid has been one way to do that,” she said. “I think we can still celebrate individual differences and some fluidity while acknowledging that these findings suggest there is also a categorical difference.”

Norris and her co-authors, WSU psychology chair Dr. David Marcus and Bradley Green of the University of Southern Mississippi, first gathered data on the sexual attraction, behavior, and identity of American adults from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), which they chose because of the size of its sample. Then, they used various forms of statistical analysis to determine if the survey respondents could be sorted into “taxons,” or groups, or if they should be spread out on a spectrum instead.

The researchers found that heterosexual and non-heterosexual adults do indeed fall into different categories, with some variation between genders and, of course, among individuals. Three percent of men and 2.7 percent of women in the sample were not heterosexual (gay, lesbian, or bisexual). The rest were straight. And the line between these two groups was not completely impermeable, but it was still clear.

Norris clarified that they did find “some fluidity” within groups—“Even in the heterosexual group, there are still a number of people who have a low-lying degree but still some degree of attraction to the same sex,” she noted—but from a population-based perspective, there are fairly clean dividing lines between adults who are straight and those who aren’t.

This conclusion contradicts popular but perhaps scientifically outdated models of sexuality as a continuum. In 1948, pioneering sex researcher Alfred Kinsey proposed a gradation of sexual experiences ranging from “exclusively heterosexual” to “equally heterosexual and homosexual” to “exclusively homosexual” on a scale from zero to six.

“Males do not represent two discrete populations, heterosexual and homosexual,” he wrote. “The world is not to be divided into sheep and goats… The living world is a continuum in each and every one of its aspects.”

The sheep-goats model, it turns out, may have been close to the truth after all. In a press release accompanying the study, Norris’s co-author David Marcus argued that the Kinsey scale has done important work in challenging homophobia but it may have ultimately been a misleading model for sex research.

“People at some point are crossing a threshold between one group and another group,” he said, referring to the division between straight and non-straight adults in the study.

“Why they do it, we can’t answer in this study. But [the fact] 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.”

But just because sexuality isn’t a continuum doesn’t mean it isn’t incredibly complicated. Some reporters, Norris noted, have oversimplified their study to make the false claim that people are either “gay or straight.”

“That’s definitely not what we’re saying,” Norris clarified. “We’re saying there is a class of people who are heterosexual and then a class that’s non-heterosexual but there’s a fantastic amount of diversity within those classes, especially that non-heterosexual class.”

The non-heterosexual class in the study does indeed display a much wider range of variation in terms of attraction, identity, and behavior than the far more homogenous heterosexual class. Simply put: The vast majority of people are straight, with their sexual identities, attractions, and behaviors lined up like ducks in a row. A small percentage of people aren’t straight, and their sexuality is far more complicated.

Patterns of attraction in the study also varied by gender in meaningful ways: Nearly 5 percent of straight women had some level of same-sex attraction compared to just 2 percent of straight men. And men who reported “some level of bisexuality” were much less likely to identify as straight than were women with self-reported bisexual attraction. Together, the authors say, these findings show that the dividing line between straight and non-straight is “more well-defined” for men than it is for women, but definitely still present for both.

The researchers also found that mental health issues—such as substance abuse, depression, anxiety, suicidal ideation, etc.—reinforced the existence of a dividing line between heterosexuality and non-heterosexuality, with straight men and women experiencing them at lower rates than their peers. Non-heterosexual men, for example, meet the diagnostic criteria for depression at twice the rate of heterosexual men—a disparity that can be attributed to enduring social stigmas around sexual orientation.

“Decades worth of research has shown that [these] mental health issues are really conferred by the stigma and pressure that’s put on non-heterosexual people in our society,” Norris said.

The authors also say that their findings lend further credence to the theory that sexual orientation has a biological basis and, therefore, cannot be changed through medically disproven techniques like conversion therapy.

“Conversion therapy is fundamentally changing who [non-heterosexual people] are,” said Marcus. “Generally we can’t do that in psychology.”