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.
Main exposure: Beliefs and attitudes about PSI measured in 1999 (12-item scale, Cronbach alpha = 0.86). Higher PSI 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.