alternatively known as the Heterosexual-Homosexual Rating Scale, was developed by Alfred Kinsey, an American biologist and sexologist, as a way to describe a person’s sexual orientation from 0 to 6. 0 is seen as being exclusively heterosexual, and 6 being exclusively homosexual; 1-5 being degrees of bisexuality between the two extremes. “X” was designated to those who indicated ‘no socio-sexual contacts or reactions’, which can be interpreted as asexuality.

The scale was revolutionary; not only did it contribute to the discussion and study of same-sex attractions, it also gave an identity and acknowledgement to those who were not exclusively heterosexual or homosexual, although Kinsey himself did not use the term “bisexual“, which at the time was popularly used to describe fauna and flora that were hermaphrodites (in the reproductive biological sense of the word). Kinsey did not believe, and his studies gave weight to this, that human sexuality was binary, but on a continuum or spectrum.