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Contraception. 2011 Feb;83(2):138-44. doi: 10.1016/j.contraception.2010.06.019. Epub 2010 Aug 23.

Longitudinal influences of friends and parents upon unprotected vaginal intercourse in adolescents.

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Department of Medicine, University of Michigan, Ann Arbor, MI 48109, USA.



Both friends and parents may influence occurrence of adolescent sexual intercourse, but these influences have not been studied together and prospectively.


We conducted a longitudinal analysis of a nationally representative sample of adolescents aged 15-18 years (n=6649), the National Longitudinal Study of Adolescent Health (Add Health). Baseline in-home and school interviews were conducted during 1995 and follow-up interviews in 1996. The main outcome measure was self-reported unprotected vaginal intercourse.


In models which adjusted for age, race, parental attitudes towards contraception and pregnancy, and adolescent sexual intercourse practices at baseline, having a friend who engaged in sexual intercourse at baseline, either unprotected (OR 2.2, 95% CI 1.6-3.2) or protected (OR 1.8, 95% CI 1.4-2.4), increased the odds of unprotected intercourse vs. never intercourse in the adolescent at follow-up (p<.001). A distant relationship with the father (OR 2.4, 95% CI 1.3-4.3) vs. a close relationship at baseline also increased the odds of unprotected intercourse at follow-up compared to never intercourse (p=.028). Parental attitudes were not associated with the outcome after consideration of the adolescent's attitudes and baseline sexual practices.


Having a friend who engages in sexual intercourse, unprotected or protected, increases the risk of unprotected intercourse. Parental attitudes are less influential after consideration of adolescent baseline attitudes and sexual practices, suggesting that parental influences are strongest before 15 years of age. Our results suggest that early intervention among both parents and adolescents may decrease the risk of unprotected intercourse.

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