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".
and the concept is one of the three main classifications of sexual orientation along with heterosexuality and homosexuality, all of which exist on the heterosexual–homosexual continuum.
A bisexual identity does not necessarily equate to equal sexual attraction to both sexes; commonly, people who have a distinct but not exclusive sexual preference for one sex over the other also identify themselves as bisexual.
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.
Kinsey studied human sexuality and argued that people have the capability of being hetero- or homosexual even if this trait does not present itself in the current circumstances.
The psychologist Jim Mc Knight writes that while the idea that bisexuality is a form of sexual orientation intermediate between homosexuality and heterosexuality is implicit in the Kinsey scale, that conception has been "severely challenged" since the publication of Homosexualities (1978), by Weinberg and the psychologist Alan P. Kinsey's 1948 work Sexual Behavior in the Human Male found that "46% of the male population had engaged in both heterosexual and homosexual activities, or 'reacted to' persons of both sexes, in the course of their adult lives".
More modern studies estimating the demographics for bisexuality have varied.Diamond, which followed women identifying as lesbian, bisexual, or unlabeled, found that "more women adopted bisexual/unlabeled identities than relinquished these identities," over a ten-year period.The study also found that "bisexual/unlabeled women had stable overall distributions of same-sex/other-sex attractions." Diamond has also studied male bisexuality, noting that survey research found "almost as many men transitioned at some point from a gay identity to a bisexual, queer or unlabeled one, as did from a bisexual identity to a gay identity." In the 1940s, the zoologist Alfred Kinsey created a scale to measure the continuum of sexual orientation from heterosexuality to homosexuality.Rather, LGB individuals are often raised in communities that are either ignorant of or openly hostile toward homosexuality.Bisexuality as a transitional identity has also been examined.