In the mid-twentieth century, Alfred Kinsey rated individuals from 0 to 6 according to their sexual orientation from heterosexual to homosexual, known as the Kinsey scale. He also included a category he called "X" for individuals with "no socio-sexual contacts or reactions". He labeled 1.5% of the adult male population as X.[27][28] In Kinsey's second book, Sexual Behavior in the Human Female, he reported this breakdown of individuals who are X: unmarried females = 14–19%, married females = 1–3%, previously married females = 5–8%, unmarried males = 3–4%, married males = 0%, and previously married males = 1–2%.[28]
Further empirical data about an asexual demographic appeared in 1994, when a research team in the United Kingdom carried out a comprehensive survey of 18,876 British residents, spurred by the need for sexual information in the wake of the AIDS pandemic. The survey included a question on sexual attraction, to which 1.05% of the respondents replied that they had "never felt sexually attracted to anyone at all." This study of this phenomenon was continued by the Canadian sexuality researcher Dr. Anthony Bogaert in 2004, who explored the asexual demographic in a series of studies. Bogaert believed that the 1% figure was not an accurate reflection of the likely much larger percentage of the population that could be identified as asexual, noting that in the initial survey 30% of people contacted chose not to participate in the survey. Since less sexually experienced people are more likely to refuse to participate in studies about sexuality, and asexuals tend to be less sexually experienced than sexuals, it is likely that asexuals were over-represented in the 30% who did not participate, compared to the 70% who did. The same study found the number of homosexuals and bisexuals combined to be about 1.1% of the population, which is much smaller than other studies indicate. However, Bogaert's sexuality research has been scrutinized in the past, since he was involved in studies that linked race to sexual behaviors as if they had an evolutionary basis. This study was highly debated by the scientific community as potentially constituting a case of scientific racism.