If you poke around the internet trying to find out how common it is for a person to be intersex, you may well wind up frustrated that nobody seems to have a precise figure to give you. You’ll probably encounter some commonly-cited odds: 1 in 2000, or 1 in 2500. People have passed these figures around for a number of years, until, by repetition, they’ve come to seem generally accepted. I used to repeat these figures myself, before I learned more about how they were generated. Being born intersex is presented as rare; less common, say, than being born with Down’s syndrome.