This page contains a brief sketch of Prof. Conway's findings on the prevalence of transsexualism.

Included are quotes of her remarks on these findings (suitable for inclusion in media reports)

Prof. Lynn Conway exposes long-standing error

in psychiatrists’ estimate of the prevalence of transsexualism:

November 7, 2005

Psychiatrists have long claimed that MtF transsexualism is extremely rare, occurring in only one in every 30,000 males.  We’ve seen that figure oft-cited in the media.  However, Professor Lynn Conway of the University of Michigan challenges that figure:

“It’s way too small, perhaps by a factor of 100”, she says. 

Counting surgeries performed over the years, Conway estimates there are now at least 40,000 postoperative trans women in the U.S. These women have transitioned out of a population of roughly 100,000,000 adult males*.  Simple division reveals that at least one in every 2500 people born as males here has undergone sex reassignment surgery (SRS):  i.e., ~ 40,000/100,000,000 = 1/2500.

However, something on the order of 5 times as many people inherently experience transsexualism than those who have already undergone sex reassignment – leading Conway to conclude the inherent condition occurs in at least one in every 500 children born as males.  Note that this figure of 1 in 500 is a lower bound on the prevalence of transsexualism (intense gender dysphoria), and the actual value could be higher.

“Those are still small numbers, but transsexualism is certainly not ‘extremely rare’”, Conway says. 

After revealing that psychiatrists have vastly underestimated the prevalence of transsexualism for many decades, Conway asks:

“Can’t psychiatrists count?”

*Note:  If we only count those adult males under age 60 (i.e., those who've typically had access to SRS in this cohort over the years), then the source population is smaller (roughly 80,000,000, leading to a larger value of the lower bound on the prevalence.

For details of Prof. Conway’s calculations see:

“How Frequently Does Transsexualism Occur?” by Lynn Conway; published on LynnConway.com, January 30, 2001.

http://ai.eecs.umich.edu/people/conway/TS/TSprevalence.html 

For more about Prof. Conway see:

http://www.lynnconway.com

http://ai.eecs.umich.edu/people/conway/BioSketch.html