title: An algorithm of smoking stages assessment in adolescents: a validation study using the latent class analysis model.
abstract: BACKGROUND
  Notwithstanding the importance of smoking stages evaluation in adolescents, there is not an appropriate instrument for its measurement. This study aims to introduce an appropriate instrument for measurement of smoking stages in adolescents and to examine its validity using latent class analysis (LCA) model.
  
  
  METHODS
  We designed an algorithm to measure the smoking stages. The relevancy and clarity of the algorithm was examined by experts and lay experts. We assessed the reliability of our algorithm using test-retest method. Moreover, using the LCA, we studied the validity of the stages measured by the designed algorithm in 4903 students (ages 14-19), who were randomly selected from grade 10 high school students in Tabriz (North-West of Iran).
  
  
  RESULTS
  The algorithm content validity indicates high relevancy and clarity percentages. Intra-class correlation of 0.929 was found in the assessment of the reliability of smoking stages (9 stages) in 154 students within a two-week interval. The LCA model revealed nine interpretable classes (G(2) = 0.051, df = 1, P = 0.821) for the measurement of smoking stages. Examination of the smoking cessation stages in a sample of 218 students in the cessation stage demonstrated that the results for five classes could be interpreted (G(2) = 0.001, df = 1, P = 0.975).
  
  
  CONCLUSIONS
  The results suggested that this algorithm is clear, valid, and reliable.
authors.affiliation: Department of Public Health, School of Health, Qazvin University of Medical Sciences, Qazvin, Iran.
authors.forename: Asghar
authors.initials: A
authors.lastname: Mohammadpoorasl
authors.affiliation: Department of Epidemiology and Biostatistics, Knowledge Utilization Research Center, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Saharnaz
authors.initials: S
authors.lastname: Nedjat
authors.affiliation: Department of Public Health, School of Health, Qazvin University of Medical Sciences, Qazvin, Iran.
authors.forename: Kamran
authors.initials: K
authors.lastname: Yazdani
authors.affiliation: Clinical Psychiatry Research Center, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Ali
authors.initials: A
authors.lastname: Fakhari
authors.affiliation: Department of Public Health, School of Health, Qazvin University of Medical Sciences, Qazvin, Iran.
authors.forename: Abbas Rahimi
authors.initials: AR
authors.lastname: Foroushani
authors.affiliation: Department of Public Health, School of Health, Qazvin University of Medical Sciences, Qazvin, Iran.
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
keywords: Adolescence; latent class analysis; reliability; smoking stages; validity