EL was classified into three categories, namely, low EL (illiteracy and primary), medium EL (middle school) and high EL (college and above). Smoking was defined as smoking one or more cigarettes per week in a recent year, and participants were classified into never smokers, former smokers and current smokers. Alcohol drinking was defined as drinking one or more alcoholic drinks per month for no less than six consecutive months, and participants were classified into never drinkers, former drinkers and current drinkers. Physical activity was classified according to the frequency of physical activity (20 min = 1 instance of activity) performed during leisure time. The categories of physical activity include exercise occasionally (< four instances of activity per week) and frequent exercise (≥ four instances of activity per week).
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