title: Validity of self reports in a cohort of Swedish adolescent smokers and smokeless tobacco (snus) users.
abstract: OBJECTIVE
  To validate self reports of cigarette and smokeless tobacco (snus) use in a prospective cohort of adolescents.
  
  
  METHODS
  A cross sectional analysis of a cohort sub-sample.
  
  
  METHODS
  County of Stockholm, Sweden.
  
  
  METHODS
  520 adolescents in the final grade of junior high school (mean age 15.0 years).
  
  
  METHODS
  Concordance between self reported tobacco use and saliva cotinine concentration.
  
  
  RESULTS
  Using a cut point of 5 ng/ml saliva cotinine to discriminate active tobacco use, there was a 98% concordance between self reported non-use in the past month and cotinine concentration. The sensitivity of the questionnaire compared to the saliva cotinine test, used as the gold standard, was 90% and the specificity 93%. One hundred and fifteen out of 520 subjects (22%) reported monthly tobacco use. Among these, 67% (46/69) of the exclusive cigarette smokers, 82% (23/28) of exclusive snus users, and 94% (15/16) of mixed users (cigarettes + snus) had cotinine concentrations above 5 ng/ml. Among subjects reporting daily use 96% (64/67) had saliva cotinine concentrations above the cut point. Exclusive current cigarette users were more likely to be classified discordantly by questionnaire and cotinine test compared to snus users (odds ratio 3.2, 95% confidence interval 1.2 to 8.6).
  
  
  CONCLUSIONS
  This study confirms the reliability of adolescents' self reported tobacco use. In a context of low exposure to environmental tobacco smoke a cut off for saliva cotinine of 5 ng/ml reliably discriminated tobacco users from non-users. Irregular use of tobacco in this age group probably explains the discrepancy between self reported use and cotinine concentrations.
authors.affiliation: Department of Public Health Sciences, Division of Social Medicine, Karolinska Institute, Stockholm, Sweden. ann.post@smd.sll.se
authors.forename: A
authors.initials: A
authors.lastname: Post
authors.forename: H
authors.initials: H
authors.lastname: Gilljam
authors.forename: I
authors.initials: I
authors.lastname: Rosendahl
authors.forename: L
authors.initials: L
authors.lastname: Meurling
authors.forename: S
authors.initials: S
authors.lastname: Bremberg
authors.forename: M R
authors.initials: MR
authors.lastname: Galanti
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology*; D015415:Biomarkers / Q000032:analysis; D003367:Cotinine / Q000032:analysis; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results; D012463:Saliva / Q000737:chemistry; D012647:Self-Assessment; D012907:Smoking / Q000453:epidemiology / Q000523:psychology*; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology; D014030:Tobacco, Smokeless
chemical_list: D015415:Biomarkers; D003367:Cotinine