The DSM-IV (1994) quotes a prevalence of roughly 1 in 30,000 assigned males and 1 in 100,000 assigned females seek sex reassignment surgery in the USA.
Those numbers are based on statistics from the 1960s, when transitioning was next to impossible, and are probably a couple orders of magnitude too low. More to the point, that threefold difference seems to be much smaller, if it exists at all.
The DSM-IV (1994) quotes a prevalence of roughly 1 in 30,000 assigned males and 1 in 100,000 assigned females seek sex reassignment surgery in the USA.
So there's a 3x factor feeding into that.