title: E-cigarettes, Cigarettes, and the Prevalence of Adolescent Tobacco Use.
abstract: Adolescent e-cigarette use has increased rapidly in recent years, but it is unclear whether e-cigarettes are merely substituting for cigarettes or whether e-cigarettes are being used by those who would not otherwise have smoked. To understand the role of e-cigarettes in overall tobacco product use, we examine prevalence rates from Southern California adolescents over 2 decades.
  
  
  
  The Children's Health Study is a longitudinal study of cohorts reaching 12th grade in 1995, 1998, 2001, 2004, and 2014. Cohorts were enrolled from entire classrooms in schools in selected communities and followed prospectively through completion of secondary school. Analyses used data from grades 11 and 12 of each cohort (N = 5490).
  
  
  
  Among 12th-grade students, the combined adjusted prevalence of current cigarette or e-cigarette use in 2014 was 13.7%. This was substantially greater than the 9.0% adjusted prevalence of current cigarette use in 2004, before e-cigarettes were available (P = .003) and only slightly less than the 14.7% adjusted prevalence of smoking in 2001 (P = .54). Similar patterns were observed for prevalence rates in 11th grade, for rates of ever use, and among both male and female adolescents and both Hispanic and Non-Hispanic White adolescents.
  
  
  
  Smoking prevalence among Southern California adolescents has declined over 2 decades, but the high prevalence of combined e-cigarette or cigarette use in 2014, compared with historical Southern California smoking prevalence, suggests that e-cigarettes are not merely substituting for cigarettes and indicates that e-cigarette use is occurring in adolescents who would not otherwise have used tobacco products.
authors.affiliation: Department of Preventive Medicine, and jtrimis@usc.edu.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Barrington-Trimis
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Robert
authors.initials: R
authors.lastname: Urman
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Leventhal
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: W James
authors.initials: WJ
authors.lastname: Gauderman
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Tess Boley
authors.initials: TB
authors.lastname: Cruz
authors.affiliation: Department of Preventive Medicine, and School of Social Work, University of Southern California, Los Angeles, California.
authors.forename: Tamika D
authors.initials: TD
authors.lastname: Gilreath
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Steve
authors.initials: S
authors.lastname: Howland
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Jennifer B
authors.initials: JB
authors.lastname: Unger
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Kiros
authors.initials: K
authors.lastname: Berhane
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Samet
authors.affiliation: Department of Preventive Medicine, and.
authors.forename: Rob
authors.initials: R
authors.lastname: McConnell
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D002140:California / Q000453:epidemiology; D066300:Electronic Nicotine Delivery Systems / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D015995:Prevalence; D011446:Prospective Studies; D012907:Smoking / Q000453:epidemiology*; D062789:Tobacco Products / Q000706:statistics & numerical data*