title: Risk of gambling onset in youth who are younger than same-grade peers.
abstract: OBJECTIVE
  To assess whether a child's age relative to the median age of classmates in the same grade is associated with the onset of gambling.
  
  
  METHODS
  Grade 7 students (n = 647) from 10 Montreal secondary schools were followed for 8 years. Relative age was expressed as years above or below the school-specific grade 7 median age. Hazard ratios and 95% confidence intervals (CI) were estimated for the association between relative age and age of gambling onset, with adjustment for sex, ethnicity, parent education, and impulsivity.
  
  
  RESULTS
  A greater proportion of students in the youngest quartile gambled compared with the oldest (85.8% vs 74.7%). Hazards of gambling onset for students younger than the median age were elevated after age 10.5 years, but hazards were protective beforehand. At age 17 years, for example, the hazard for gambling onset was 61% greater (95% CI 1.4-1.9) for youth who were 1 year younger, but at age 8 years the hazard was 23% lower (95% CI 0.7-0.9).
  
  
  CONCLUSIONS
  Younger relative age may be a risk factor for gambling onset in older youth.
authors.affiliation: Institut national de santé publique du Québec, Montréal, Canada. nathalie.auger@inspq.qc.ca
authors.forename: Nathalie
authors.initials: N
authors.lastname: Auger
authors.forename: Ernest
authors.initials: E
authors.lastname: Lo
authors.forename: Jennifer
authors.initials: J
authors.lastname: O'Loughlin
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D017668:Age of Onset; D002648:Child; D005260:Female; D005715:Gambling / Q000453:epidemiology*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D010379:Peer Group; D011792:Quebec / Q000453:epidemiology; D012307:Risk Factors; D012737:Sex Factors; D013334:Students / Q000706:statistics & numerical data; D055815:Young Adult