Reliability of a questionnaire on substance use among adolescent students, Brazil.
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.
Machado Neto
Adelmo de Souza
Ade S
Departamento de Medicina, Faculdade de Medicina da Bahia, Universidade Federal da Bahia, Salvador, BA, Brasil. machadonetoa@yahoo.com.br
Andrade
Tarcisio Matos
TM
Fernandes
Gilênio Borges
GB
Zacharias
Helder Paulo
HP
Carvalho
Fernando Martins
FM
Machado
Ana Paula Souza
AP
Dias
Ana Carmen Costa
AC
Garcia
Ana Carolina Rocha
AC
Santana
Lauro Reis
LR
Rolin
Carlos Eduardo
CE
Sampaio
Cyntia
C
Ghiraldi
Gisele
G
Bastos
Francisco Inácio
FI
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