human 27 female 25 Humans 23 male 23 Female 21 adult 21 heterosexuality 18 Male 17 major clinical study 14 sexual behavior 14 Adult 13 Sexual Behavior 12 article 12 Middle Aged 11 middle aged 11 psychology 10 Gender studies, gender groups 9 Heterosexuality 9 sexual and gender minority 8 Article 7 Sexual Partners 7 controlled study 7 sexuality 7 Adolescent 6 Gay & Lesbian studies 6 HIV Infections 6 Human immunodeficiency virus infection 6 Sexual orientation 6 Surveys and Questionnaires 6 Young Adult 6