Bem based this theory in part on the finding that a majority of gay men and lesbians report being gender-nonconforming during their childhood years. A meta-analysis of 48 studies showed childhood gender nonconformity to be the strongest predictor of a homosexual orientation for both men and women. Bem also noted that in a study by the Kinsey Institute of approximately 1000 gay men and lesbians (and a control group of 500 heterosexual men and women), 63% of both gay men and lesbians reported that they did not like activities typical of their sex in childhood, compared with only 10–15% of heterosexual men and women. Bem also drew from six prospective studies, longitudinal studies that began with gender-nonconforming boys around age 7 and followed them into adolescence and adulthood; a majority (63%) of the gender nonconforming boys become gay or bisexual as adults.