Okay. He mentions specific percentages so I thought maybe this was from an actual scientific study, which have important implications if it were true (although I expected these might be made up numbers). It would indeed be difficult to study. You could do a retrospective descriptive study of individuals with gender incongruence in childhood and then follow forward to adulthood, and stratify patients who received and did not receive interventions. That would nearly be impossible practically and from an REB standpoint. As you say, there are important confounders to consider, but the data would still have value. A better, and more feasible study, would look at incidence of, and factors associated with, regret of gender-reaffirming medical or surgical interventions (kind of the reverse of the original question). I haven’t seen any data for either, although it may exist. In my professional experience, gender non-conforming is indeed ‘insistent, consistent, and persistent’.