sample size was calculated at 384 persons6
(plus 20% for possible attrition, was 460
cases) and sampling was by convenience
method. Data collection was collected on
four occasions, and there were different
samples on each occasion: 426 the first time,
334 the second time, 367 the third time,
and 361 the fourth time. The study was
approved by the Human Ethic Committee of
Thammasat University, Faculty of Medicine,
and informed consent was obtained from the
study participants.