A 2002 survey in the United States by National Center for Health Statistics found that 1.8 percent of men ages 18–44 considered themselves bisexual, 2.3 percent homosexual, and 3.9 percent as "something else".
The same study found that 2.8 percent of women ages 18–44 considered themselves bisexual, 1.3 percent homosexual, and 3.8 percent as "something else".
Some individuals identify themselves as heterosexual, homosexual or bisexual without having had any sexual experience.
Others have had homosexual experiences but do not consider themselves to be gay, lesbian, or bisexual.
Magnus Hirschfeld argued that adult sexual orientation can be explained in terms of the bisexual nature of the developing fetus: he believed that in every embryo there is one rudimentary neutral center for attraction to males and another for attraction to females.