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.
Prospective cohort study.
The Growing Up Today Study, a longitudinal cohort study of adolescents.
A total of 11 448 adolescents aged 12 to 17 years who reported in 1999 that they had never had sexual intercourse.
Beliefs and attitudes about PSI measured in 1999 (12-item scale, Cronbach α = 0.86). Higher PSI scale scores indicated stronger beliefs about postponing sex.
Sexual intercourse reported on the 2000 survey.
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.
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.