From 2008 to 2010, 14 countries, most of them being either low or middle income with a heavy burden of tobacco use and highly populated, conducted the Global Adult Tobacco Survey (GATS) to monitor tobacco use in their countries and the changes driven by policies enacted in those nations . Selected as one of the 14 countries, Thailand conducted GATS in 2009 [8, 9]. To ensure useful comparisons across the 14 countries, the survey followed the standard GATS protocol.
The target population was noninstitutionalized residents, in Thailand, aged 15 years or above (defined as adults in the current study), and the sample was a nationally and regionally representative probability sample. A stratified three-stage cluster sampling design was used with the strata being five geographic regions: the Bangkok metropolitan area and the North, Northeast, Central, and South regions of Thailand which were further stratified into urban and rural areas. The sampling frame used was supplied by the National Statistical Office (NSO), derived from Thailand’s National Population and Housing Census 2000 . Primary sampling units (PSUs) were blocks in urban areas and villages in rural areas and were randomly selected, in the first stage, using selection probability proportional to size sampling. In the second stage, 16 and 28 households were randomly chosen from the previously selected urban or rural PSUs, respectively, using simple systematic sampling. In the third stage, a face-to-face screening interview was used at each randomly selected household, in which a list of all eligible individuals in the household was drawn up and one person from the list was randomly selected to participate in the interview, using an algorithm of simple random sampling on the handheld device designed for data collection. If the respondent was not available, the interviewer would schedule another appointment to interview. Three attempts were made before the individual was considered a nonrespondent. If a residence was found to be empty, it was declared to be ineligible; if a selected respondent refused to participate, the individual was considered to be a nonrespondent.
All interviewees were informed that they could stop the survey and the response was confidential. Interviewers were selected by provincial statistical offices (PSO) and were only responsible for their own province, with supervisors from corresponding PSOs. Both interviewers and supervisors had experience on national health related surveys fieldwork. All of them had at least a Bachelor’s degree in education. There were 2 interviewers/supervisors - training sessions using the same trainers with technical support from CDC and WHO experts.
The interview was conducted in the selected household; while other members of the household could be present, they were instructed to remain silent during the interview. No proxy responding was allowed and no incentives were provided for participation. For the questionnaire interview (average duration was 19.1 minutes, SD = 7.6 minutes), the trained interviewers used personal digital assistants (PDAs) to collect data. The fieldwork started on February 1, 2009, and was completed on May 31 of the same year.
The questionnaire included information on demographics (age, gender, education, income); use of smoking tobacco and of smokeless tobacco; cessation attempts and interest in quitting; exposure to secondhand smoke; purchase of cigarettes during the last 30 days; exposure to media that provided information on smoking and health effects; questions about pictorial warning labels on manufactured cigarette packs, and knowledge, attitudes, and perceptions about tobacco use. Some questions were added by the Thailand GATS working group and reviewed by the Thailand GATS expert committee . GATS protocols were approved by the Ethics Committee of the Faculty of Public Health, Mahidol University.
Definition of variables
Used as an indicator of socioeconomic status, total personal income was grouped as low (less than 4,780 baht or less than 140.6 USD per month), middle (4,780 to 7,000 baht or 140.6 to 205.9 USD per month), and high (7,001 baht or higher or 206.0 USD or higher per month). Education was grouped into none or less than primary school, primary school, secondary school and university and above. RYO cigarettes, also known as hand-rolled cigarettes are referred to the cigarettes made by hand using shredded tobacco and papers. Current smoking was defined as responding yes to a question about smoking daily or less than daily. Whether smoking can cause seven well proved diseases, including stroke, heart stack, lung cancer, mouth cancer, larynx cancer, impotence, emphysema, was used as information to assess the extent of participants knowledge of health effects. A knowledge score, defined as the total number of the seven knowledge items answered correctly, was used as a summary measure of knowledge.
The data were reviewed for inconsistencies and out of range responses, edited, and weighted, using the complex survey analysis module of SPSS Version 18. Weights were computed as a product of three components: base weight, which was an inverse of the final probability of selection, adjustment for nonresponse at both the household and individual level, and post-stratification adjustment based on residence (urban or rural), age, and gender from the 2008 population projection for Thailand. A two sample test was used for pair comparison of prevalence among different group of users at statistically significant level of p < 0.05. Analyses of knowledge, addiction, and quitting, as well as multivariate analysis, were carried out for men only, because the levels of use of the tobacco products among females were too low for reliable analyses. Multivariate analyses, taking the complex sample design into account, used logistic regression models to see if the type of cigarettes smoked (manufactured cigarette only, RYO only and dual use) was associated with age, education, income, residence, and region. These variables were selected because of previous studies that have shown these variables to be related to tobacco use and the use of RYO. In the multivariate models, we determined the relationship of one variable while controlling for the effects of the others. The test for importance of a factor was carried out by a comparison of the full model with all factors and a reduced model where the factor of interest was excluded.