Equal intervals were assumed between the single categories, except for X. Kinsey used seven categories (0–6) to classify sexual orientation as a continuum plus an additional category labeled X (no socio-sexual contacts or reactions). It assesses both overt sexual behaviour as well as sexual fantasies. The scale was used to classify and quantify homosexual and heterosexual behaviour across the American population. The two books are often referred to as 'the Kinsey Reports'. The Kinsey scale (also Kinsey homosexual-heterosexual scale) was first presented by Alfred Kinsey in his two influential books Sexual Behavior in the Human Male (1948) and Sexual Behaviour in the Human Female (1953).
