Cigarettes were separated into two types: yamuan
(hand-rolled cigarettes using locally grown tobacco) and
manufactured cigarettes (both filter and non filter). The
following smoking status categories used were: never
smoker (lifetime never smoker or had smoked for less
than one year before the enrollment date or smoked fewer
than one cigarette per day), ex-smoker (smoked for at
least one year and smoked at least one cigarette per day
and had quit for at least one year before the enrollment
date) and current smoker (smoked for at least one year
and smoked at least one cigarette per day and either never
quit or quit less than one year before the enrollment date).
Dose (cigarettes per day) was calculated by dividing the
number of cigarettes smoked in a week by 7, in a month by
30 and in a period longer than one month by 35. Yamuan
dose was multiplied by 1.5 owing to their longer length
compared with a regular cigarette (Sriamporn et al., 2002).
Smokers were then divided into three groups: less than
10, 10-15 and more than 15 cigarettes per day.