I'm 100% sure you're correct in accordance with modern studies, but I also think identifying as 'transgendered' requires a certain level of social solvency and neutral selection bias, which the majority of the world doesn't have. For example, a Chinese/Indian rice farmer (only about two billion people or so) doesn't give a flying fuck if they're transgendered or not, because they've got a gangrenous foot, and need to pick this bushel of rice so they can trade it on the black market for some penicillin. This is more or less the survival urgency required of +/- 75% of the worlds total population. I imagine if you look at the people who have enough to spend time sitting around doing nothing productive (The western world, Japan, our various satellites.) you have a total population of something like 2 billion people. Plus, most of the highly-populace regions also have negative stigma for transgendered people. For example, in Nigeria, if you're trans and get caught, you get beheaded. It's essentially the same deal in most of the 3rd world.  I'd argue that they probably have a rate of incidence on the order of magnitude of homosexuals, probably somewhere in the upper single digits.