title: Increased risks of early sexual initiators: time makes a difference.
abstract: BACKGROUND
  Years since onset of sexual intercourse (YSSI) is a rarely used variable when studying adolescents' sexual outcomes. The aim of this study is to evaluate the influence of YSSI on the adverse sexual outcomes of early sexual initiators.
  
  
  METHODS
  Data were drawn from the 2002 Swiss Multicenter Adolescent Survey on Health database, a nationally representative cross-sectional survey including 7429 adolescents in post-mandatory school aged 16-20 years. Only adolescents reporting sexual intercourse (SI) were included (n=4388; 45% females) and categorised by age of onset of SI (early initiators, age <16: n=1469, 44% females; and late initiators, age ≥ 16: n=2919, 46% females). Analyses were done separately by gender. Groups were compared for personal characteristics at the bivariate level. We analysed three sexual outcomes (≥ four sexual partners, pregnancy and condom non-use at last SI), controlling for all significant personal variables with two logistic regressions using first age, then YSSI as one of the confounding variables. Results are given as adjusted odds ratios (AOR) using late initiators as the reference category.
  
  
  RESULTS
  After adjusting for YSSI instead of age, negative sexual outcomes among early initiators were no longer significant, except for multiple sexual partners among females, although at a much lower level. Early initiators were less likely to report condom non-use at last SI when adjusting for YSSI (females: AOR=0.59 [0.44-0.79], P<0.001; males: AOR=0.71 [0.50-1.00], P=0.053).
  
  
  CONCLUSIONS
  YSSI is an important explanatory variable when studying adolescents' sexuality and needs to be included in future research on adolescents' sexual health.
authors.affiliation: Research Group on Adolescent Health, Institute of Social and Preventive Medicine (IUMSP), Centre Hospitalier Universitaire Vaudois, University of Lausanne, Bugnon 17, 1005 Lausanne, Switzerland.
authors.forename: Philippe
authors.initials: P
authors.lastname: Baumann
authors.forename: Richard E
authors.initials: RE
authors.lastname: Bélanger
authors.forename: Christina
authors.initials: C
authors.lastname: Akre
authors.forename: Joan-Carles
authors.initials: JC
authors.lastname: Suris
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002650:Child Abuse, Sexual / Q000523:psychology / Q000706:statistics & numerical data; D003075:Coitus / Q000523:psychology*; D017280:Condoms / Q000706:statistics & numerical data; D003430:Cross-Sectional Studies; D003866:Depressive Disorder / Q000453:epidemiology / Q000523:psychology; D005260:Female; D006306:Health Surveys; D006801:Humans; D016015:Logistic Models; D008297:Male; D011247:Pregnancy; D011275:Pregnancy, Unwanted / Q000523:psychology*; D012307:Risk Factors; D012747:Sexual Partners / Q000523:psychology; D013557:Switzerland; D047568:Unsafe Sex / Q000523:psychology* / Q000706:statistics & numerical data; D055815:Young Adult