I’m interested in where the figure of one in 20,000
Say the UK population is 60,000,000. 1 in 20,000 gives 3000 people.
If you look in uktrans.info/grc-stats you'll find this:
As of the end of June 2015, since the Gender Recognition Act 2004 came into force (April 2005):
- 4,631 applications have been received
- 3,999 full Gender Recognition Certificates have been issued by the GRP
The 1 in 20,000 figure will be something like that. My immediate thought on hearing "1 in 20,000" was "hmmm, you are thinking about what's going on in your immediate scientific realm rather than actually seeing what's happening in the real world".
Scientists can provide useful knowledge but they can be very blinkered when there's a political dimension.