title: Sexual initiation, substance use, and sexual behavior and knowledge among vocational students in northern Thailand.
abstract: BACKGROUND
  Thailand has undergone dramatic social changes in the last two decades, yet little is known about factors related to sexual initiation among adolescents.
  
  
  METHODS
  A survey using the audio computer-assisted self-interviewing method was conducted to assess social and demographic characteristics, substance use, sexual behavior, and knowledge of HIV and STIs among 1,725 vocational school students aged 15-21 living in northern Thailand. Gender differences for these factors were evaluated using chi-square and Mann-Whitney U tests. Multivariate survival analysis using Cox proportional hazards models assessed associations between these variables and sexual initiation for each gender.
  
  
  RESULTS
  Males initiated sexual intercourse at an earlier age than females (median ages of 17 and 18, respectively). At any given age, sexual initiation was associated with having a nonagricultural background and using alcohol or methamphetamine (adjusted rate ratios, 1.3-2.9). For males, initiation was also associated with having parents who did not live together, having a friend as a confidant, tobacco use, high perceived risk for HIV and high STI knowledge (1.3-1.7). For females, other factors associated with earlier initiation were younger age at interview, living away from family, lacking a family member as a confidant, high perceived risk for STIs and ever having smoked marijuana (1.3-2.4).
  
  
  CONCLUSIONS
  Interventions to ameliorate the adverse consequences of early sexual initiation need to address social influences such as parents and peer groups. Programs should identify and target high-risk subgroups, such as those who are sexually experienced at an early age and those engaged in patterns of generalized risk-taking.
authors.affiliation: Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: Alice
authors.initials: A
authors.lastname: Liu
authors.forename: Peter
authors.initials: P
authors.lastname: Kilmarx
authors.forename: Richard A
authors.initials: RA
authors.lastname: Jenkins
authors.forename: Chomnad
authors.initials: C
authors.lastname: Manopaiboon
authors.forename: Philip A
authors.initials: PA
authors.lastname: Mock
authors.forename: Supaporn
authors.initials: S
authors.lastname: Jeeyapunt
authors.forename: Wat
authors.initials: W
authors.lastname: Uthaivoravit
authors.forename: Frits
authors.initials: F
authors.lastname: van Griensven
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000208:ethnology*; D000328:Adult; D000367:Age Factors; D003430:Cross-Sectional Studies; D005260:Female; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D008297:Male; D010379:Peer Group; D016016:Proportional Hazards Models; D012309:Risk-Taking; D012725:Sexual Behavior / Q000208:ethnology*; D012749:Sexually Transmitted Diseases / Q000453:epidemiology / Q000517:prevention & control; D012922:Social Change; D012925:Social Conformity; D013334:Students / Q000523:psychology* / Q000706:statistics & numerical data; D019966:Substance-Related Disorders / Q000453:epidemiology / Q000517:prevention & control; D011795:Surveys and Questionnaires; D013785:Thailand / Q000453:epidemiology; D014584:User-Computer Interface