Humans 52 Sexual Partners human 52 sexuality 52 adult 49 male 46 Adult 45 female 43 Male 41 Female 40 Young Adult 32 psychology 32 young adult 32 sexual behavior 28 Sexual Behavior 27 adolescent 25 article 25 Adolescent 24 major clinical study 20 HIV Infections 19 Human immunodeficiency virus infection 19 Interpersonal Relations 17 human relation 17 middle aged 17 Middle Aged 16 human experiment 15 Human immunodeficiency virus 13 Longitudinal Studies 11 controlled study 11 longitudinal study 11