title: Beyond age at first sex: patterns of emerging sexual behavior in adolescence and young adulthood.
abstract: OBJECTIVE
  Although the emergence of sexual expression during adolescence and early adulthood is nearly universal, little is known about patterns of initiation.
  
  
  METHODS
  We used latent class analysis to group 12,194 respondents from waves I and IV of the National Longitudinal Study of Adolescent Health (Add Health) into one of five classes based on variety, timing, spacing, and sequencing of oral-genital, anal, and vaginal sex. Multinomial logistic regression models, stratified by biological sex, examined associations between sociodemographic characteristics and class membership.
  
  
  RESULTS
  Approximately half of respondents followed a pattern characterized predominately by initiation of vaginal sex first, average age of initiation of approximately 16 years, and spacing of >1 year between initiation of the first and second behaviors; almost one-third initiated sexual activity slightly later but reported first experiences of oral-genital and vaginal sex within the same year. Classes characterized by postponement of sexual activity, initiation of only one type of behavior, or adolescent initiation of anal sex were substantially less common. Compared with white respondents, black respondents were more likely to appear in classes characterized by initiation of vaginal sex first. Respondents from lower socioeconomic backgrounds were more likely to be in classes distinguished by early/atypical patterns of initiation.
  
  
  CONCLUSIONS
  A small number of typical and atypical patterns capture the emergence of sexual behavior during adolescence, but these patterns reveal complex associations among different elements of emerging sexuality that should be considered in future research.
authors.affiliation: AAAS/APA Executive Branch Fellow, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA. aahaydon@gmail.com
authors.forename: Abigail A
authors.initials: AA
authors.lastname: Haydon
authors.forename: Amy H
authors.initials: AH
authors.lastname: Herring
authors.forename: Mitchell J
authors.initials: MJ
authors.lastname: Prinstein
authors.forename: Carolyn Tucker
authors.initials: CT
authors.lastname: Halpern
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D000328:Adult; D003075:Coitus; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D012725:Sexual Behavior / Q000706:statistics & numerical data*; D046468:Sexual Development; D014481:United States; D055815:Young Adult