he 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 [10].
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.