I wouldn't put much credence into the author Dr. Vernon Coleman. He is a rather prolific writer in several, unrelated yet culturally "popular" fields. He thinks that vaccines are not safe, that people can use their minds to heal their bodies, there are several books about how doctors and nurses kill us and how to avoid this, etc. He seems to mostly mistrust the medical profession and this is the only book that touches on cross-gender expression, out of several hundred books and articles he has written:

http://www.amazon.com/s/ref=series_r...3Ddigital-text
http://www.vernoncoleman.com/main.htm

In the Amazon preview, it says that he surveyed just over 1,000 British males, but it is unclear how he did this (from the preview). Did he seek participants in some of the tabloids that he contributes to which would then provide him with a self-assessed cohort? This would not be a random study and it would be impossible to estimate any percentages of men who crossdress to the general population.

There are close to 30,000 people who've joined this forum since its inception according to the numbers on the index page, possibly more if the numbers were culled at one point. This does not mean that 10% or 50% of the population crossdresses.