title: Reliability of a questionnaire on substance use among adolescent students, Brazil.
abstract: OBJECTIVE
  To analyze reliability of a self-applied questionnaire on substance use and misuse among adolescent students.
  
  
  METHODS
  Two cross-sectional studies were carried out for the instrument test-retest. The sample comprised male and female students aged 1119 years from public and private schools (elementary, middle, and high school students) in the city of Salvador, Northeastern Brazil, in 2006. A total of 591 questionnaires were applied in the test and 467 in the retest. Descriptive statistics, the Kappa index, Cronbach's alpha and intraclass correlation were estimated.
  
  
  RESULTS
  The prevalence of substance use/misuse was similar in both test and retest. Sociodemographic variables showed a "moderate" to "almost perfect" agreement for the Kappa index, and a "satisfactory" (>0.75) consistency for Cronbach's alpha and intraclass correlation. The age which psychoactive substances (tobacco, alcohol, and cannabis) were first used and chronological age were similar in both studies. Test-retest reliability was found to be a good indicator of students' age of initiation and their patterns of substance use.
  
  
  CONCLUSIONS
  The questionnaire reliability was found to be satisfactory in the population studied.
authors.affiliation: Departamento de Medicina, Faculdade de Medicina da Bahia, Universidade Federal da Bahia, Salvador, BA, Brasil. machadonetoa@yahoo.com.br
authors.forename: Adelmo de Souza
authors.initials: Ade S
authors.lastname: Machado Neto
authors.forename: Tarcisio Matos
authors.initials: TM
authors.lastname: Andrade
authors.forename: Gilênio Borges
authors.initials: GB
authors.lastname: Fernandes
authors.forename: Helder Paulo
authors.initials: HP
authors.lastname: Zacharias
authors.forename: Fernando Martins
authors.initials: FM
authors.lastname: Carvalho
authors.forename: Ana Paula Souza
authors.initials: AP
authors.lastname: Machado
authors.forename: Ana Carmen Costa
authors.initials: AC
authors.lastname: Dias
authors.forename: Ana Carolina Rocha
authors.initials: AC
authors.lastname: Garcia
authors.forename: Lauro Reis
authors.initials: LR
authors.lastname: Santana
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: Rolin
authors.forename: Cyntia
authors.initials: C
authors.lastname: Sampaio
authors.forename: Gisele
authors.initials: G
authors.lastname: Ghiraldi
authors.forename: Francisco Inácio
authors.initials: FI
authors.lastname: Bastos
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D001938:Brazil / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D015203:Reproducibility of Results; D012959:Socioeconomic Factors; D013334:Students / Q000706:statistics & numerical data*; D019966:Substance-Related Disorders / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D014505:Urban Population; D055815:Young Adult