.
WPATH essentially says that many crossdressers and other transgender people have, to some degree, a gender identity which does not match the sex assigned to them at birth.
They also say in their "Standards of Care," that "gender identity... [is] understood to be firmly established by age 4, though for some transgender individuals, gender identity may remain somewhat fluid for many years."
(From http://www.wpath.org/site_page.cfm?p...n_webpage=3947 ).
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WPATH, formerly known as the Harry Benjamin International Gender Dysphoria Association, wrote the Standards of Care for the Health of Transsexual, Transgender, and Gender Nonconforming People.
WPATH's web site is at www.WPATH.org .
A PDF of The Standards of Care, version 7 (2011), is at
http://www.wpath.org/uploaded_files/...0SOC,%20V7.pdf .
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I am a retired Computer Programmer, formerly with a large corporation, and part of my job was recommending which hardware and software the company should buy.
Another part of my job was doing research on various things, and then providing the company with the results of my research.
If I had just given them my opinions (recommendations) about what they should buy, but not provided any documentation about how I developed my recommendations, they would have told me that they needed documentation showing how I developed my recommendations.
The same was true when I was in college. My professors did not want just my opinions, but supporting documentation about how I developed those opinions.
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