@DadJoke do you agree one would have to define "transgender" clearly in order to see if someone would be counted in any study as such?
Would anyone who doesn't consider themselves to have a gender identity that "matches" their sex count as trans or not trans? (The person themselves would have to be confident of knowing this as well, to work out how they identify).
In working out which genders match which sexes (or not) do you agree there needs to be consensus on which match with which?
We are told that women are both male or female, so presumably either sex "matches" a woman gender identity. But that would mean no-one is trans. So the definition needs clarification.
Of course, if you think you'll get accurate data on terms that are never defined you won't be interested in establishing this, but most would disagree.