GYTS, a self-administered school-based survey, uses a 2-stage cluster sample design that is grade-based and produces representative samples of students with ages ranging from 10 to 17 years. A subset of students aged 13 to 15 years is used for comparing the data within and across Word Health Organization (WHO) regions. In countries, such as small islands, where all students in the selected grades were surveyed, a census rather than a 2-stage cluster sample is conducted. The survey methods are described in detail elsewhere (6
Eligible countries were selected on the basis of the following inclusion criteria: a nationally representative sample, recent completion of GYTS (2007–2009), large sample size (≥3,000 participants), and GYTS data publicly released. Of 35 eligible countries that met the inclusion criteria, 1 country from each WHO region was randomly selected for this study. Data analysis was performed on a subset of participants aged 13 to 15 years (n) among all ages in the grades selected for the survey (N). The selected countries and the year GYTS was conducted (values for n and N) are as follows: Ghana, 2009 (n/N = 4,171/8,295); Guatemala, 2008 (n/N = 3,838/5,565); Saudi Arabia, 2007 (n/N = 2,574/3,829); the Philippines, 2007 (n/N = 3,278/5,919); Slovakia, 2007 (n/N = 4,176/4,696); and Thailand, 2009 (n/N = 7,649/9,963).
Some questions from the GYTS presented the opportunity for participants to contradict themselves when responding (). Self-reported cigarette smoking on 1 or more of the past 30 days was used to determine cigarette smoking status. For this series of questions, 5 approaches were taken for handling inconsistent responses to questions regarding cigarette use: GYTS, do-nothing, gatekeeper, global, and preponderance ().
Selected Global Youth Tobacco Survey (GYTS) Questions and Data Edit Approaches
We used Stata 11 software (StataCorp LP, College Station, Texas) to account for complex survey design and to calculate weighted point estimates and standard error (SE) of the estimates. Estimates with a relative SE (ratio of the SE of the estimate to the estimate, multiplied by 100) greater than 30% were considered statistically unreliable. Adjusted Wald tests were used to evaluate for statistical differences between point estimates derived from the GYTS approach and the 4 other data editing approaches. Significance was set at P < .05.