Predicting sexual initiation in a prospective cohort study of adolescents

Objective: To determine whether a new scale measuring beliefs about postponing sexual initiation (PSI) predicts sexual initiation and whether the association between PSI and sexual initiation is mediated by intention to initiate sexual intercourse. Design: Prospective cohort study. Setting: The Growing Up Today Study, a longitudinal cohort study of adolescents. Participants: A total of 11 448 adolescents aged 12 to 17 years who reported in 1999 that they had never had sexual intercourse. MainExposure: Beliefs and attitudes about PSI measured in1999(12-item scale, Cronbach alpha = 0.86). HigherPSI scale scores indicated stronger beliefs about postponing sex. Outcome Measure: Sexual intercourse reported on the 2000 survey. Results: The mean (SD) age of participants was 14.3 (1.5) years, and 94.4% were white. Of the participants, 7.5% of boys and 10.1% of girls initiated sexual intercourse between 1999 and 2000. The PSI scale score was inversely associated with intention to initiate sex and with sexual initiation in boys and girls (P <. 001 for both). Intention to initiate sex was positively associated with sexual initiation (P <. 001). In multivariate models, PSI scale scores were inversely associated with sexual intercourse initiation in boys ( odds ratio, 0.90 for a 1-U increase in PSI scale score; 95% confidence interval, 0.87-0.93; P <. 001) and girls (odds ratio, 0.91; 95% confidence interval, 0.89-0.93; P <. 001). The strength of the association decreased when intention to initiate sexual intercourse was added to both models. Conclusion: A new scale measuring beliefs and attitudes about PSI predicted sexual intercourse initiation in the next year, and intention to initiate sex mediated this association.