60%
Doesn't surprise me though as I was in Thailand for a few weeks last month and one of my friends introduced me to a girl at a bar who I thought was a chick but he knew otherwise.
He told me a couple of minutes later and I literally couldn't believe it as he/she was ridiculously convincing, I had to fully put the question "are you or have you ever been a boy?" to which he/she nodded.
Lucky escape for me, not so lucky for the guy I saw in the same bar the following night taking that ladyboy home. I caught eyes with he/she as they were leaving and we just grinned about what was happening. Classic.