They cited a wide body of studies, including studies which included only trans kids. All studies produced consistent results. For those who didn't read the full article, here's the preamble to the 80% figure quoted above:
>There have, however, been almost a dozen studies of looking at the rate of "desistance," among trans-identified kids—which, in this context, refers to cases in which trans kids eventually identify as their sex at birth. Canadian sex researcher James Cantor summarized those studies' findings in a blog post: "Despite the differences in country, culture, decade, and follow-up length and method, all the studies have come to a remarkably similar conclusion: Only very few trans-kids still want to transition by the time they are adults. Instead, they generally turn out to be regular gay or lesbian folks." The exact rate of desistance varied by study, but overall, they concluded that about 80 percent trans kids eventually identified as their sex at birth.
They cited various problems with the other studies.
All of Cantor's sources included non conforming behavior or "sub threshold" gender identity disorder.[1] He just ignored the numbers lost to follow up. And several studies found predictors of persistence. Like meeting the criteria for gender identity disorder.[2]
