On the 80% (which is really closer to 99%):
GIRES submitted evidence to the Trans Equality Inquiry in 2015 at which they stated that of an estimated trans population of 1% of the populace, only 5% of that 1% had sought any medical assistance at all.
That is, only 5 of 100 persons identifying as trans had gone to their GP about being trans.
GIRES then estimated that by 2020 around 20% in total would eventually seek help from health care professionals.
This estimate was based on figures from trans populations in other countries where studies researched the issue.
I think that estimate is wildly off and the real number will be much smaller, because those studies looked into transsexuals and those with gender dysphoria and not the now much more prevalent transgender population, a majority of whom insist that one does not need to have GD to be trans.
Please note that seeking help from health care professionals does not equate to genital surgery.
In an ideal world, one where HCPs seek the best outcome for anyone with GD, the steps are:
-diagnosis
-therapy
-cross-sex hormones plus suppressants of one's natural hormones
-hair removal
-speech therapy
-a range of other non-genital surgeries ranging from shaving down an Adam's apple to facial feminisation surgeries to breast implants for men
-mastectomies and chest shaping for women
-removal of gonads for men and women
-hysterectomy
-finally, genital construction surgeries that involve removal and reshaping of existing organs and constructing of facsimile of those of the opposite sex
In terms of prevalence, imagine the first medical step (diagnosis) as the base of a pyramid and the complete genital surgery as the very top. So that theoretical 20% who seek any help at all are not all going on to complete genital surgery.
The last time I looked this up, I found one study that didn't just show how few patients even proceeded to genital surgeries at all (