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Nearly 2,200 identified as transgender or gender nonconforming. The study found that these kids reported worse mental and physical health than other kids, echoing results seen in previous research. Bullying and discrimination are among possible reasons for the differences, Rider said, although the survey didn’t ask.

Rider said it’s a study based on a statewide population of teens in ninth and 11th grades and that the results can be used to estimate numbers of trans and gender nonconforming teens in those grades across the United States.

The study was published Monday in Pediatrics.

Although the study only included teens in two grades, the rates are higher than a UCLA study released last year estimating that 0.7 per cent of teens aged 13 to 17 are transgender, or about 150,000 kids. That study used government data on adults to estimate numbers for children. It said 0.6 per cent of U.S. adults identify as transgender, or about 1.4 million.

Some experts believe rising awareness of transgender issues has led increasing numbers of transgender teens to come out, or to experiment with gender identification.

“With growing trans visibility in the United States, some youth might find it safer to come out and talk about gender exploration,” Rider said.

But differences in estimates may also reflect differences in how gender identity questions are phrased, Rider said.

The federal Centers for Disease Control and Prevention has not asked about transgender status on its youth surveys, noting that it is difficult to find the right question to yield a credible answer.