Gender composition of friendship networks and age at first intercourse: a life-course data analysis

We investigate the impact of some characteristics of friendship networks on the timing of the first sexual intercourse. We assume that the gender-segregated composition of such networks explains part of the particularly late age at first intercourse in Italy. We use new data from a survey on sexual behavior and reproductive health of Italian first and second-year university students. The survey has been carried out in 15 different universities in 2000-2001 and it includes retrospective data on age at first intercourse, as well as retrospectively-collected time-varying measures for the gender composition of the friendship network at different ages, for almost 5,000 cases. After having described the data as transition frequencies, we use a Cox proportional hazards model with time-varying covariates. Results are in accordance with the hypothesis that having friendship networks that include more members of the other gender and talking about sex with friends increases the relative risk of first sexual intercourse.