title: A discrete time hazards model of smoking initiation among West Coast youth from age 5 to 23.
abstract: OBJECTIVE
  To identify factors associated with age of smoking initiation and distinguish vulnerable periods for initiation according to those factors.
  
  
  METHODS
  Discrete time hazards analysis was used to model smoking initiation as a function of age (5-23), demographic and familial influence variables (measured at age 13), and their interactions in a cohort of 6255 youths who completed six assessments over a 10-year period from age 13 to 23 years.
  
  
  RESULTS
  Half of the sample had initiated smoking by age 13, and the hazard for initiation was greatest between ages 13 and 15. In addition to differences associated with race/ethnicity, protective factors for smoking initiation included high parental education and having an intact family of origin. Having an older sibling and participant's exposure to smoking by an important adult were both risk factors, with the latter having a stronger effect for females and Blacks. For all effects, the strength of the association differed across the age range.
  
  
  CONCLUSIONS
  The impact of demographic and family influence factors on smoking initiation varies over time. However, the maximum risk for initiation is during the early teen years, and the range of considerable vulnerability is during middle school and high school.
authors.affiliation: RAND Corporation, Behavioral and Social Sciences Group, 1776 Main Street, PO Box 2138, Santa Monica, CA 90407-2138, USA. orlando@rand.org
authors.forename: Maria Orlando
authors.initials: MO
authors.lastname: Edelen
authors.forename: Joan S
authors.initials: JS
authors.lastname: Tucker
authors.forename: Phyllis L
authors.initials: PL
authors.lastname: Ellickson
mesh_terms: D000206:Actuarial Analysis; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002140:California; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D009922:Oregon; D011336:Probability; D016016:Proportional Hazards Models; D018570:Risk Assessment / Q000706:statistics & numerical data; D012907:Smoking / Q000453:epidemiology*; D000074606:Smoking Prevention; D012931:Social Environment