Demographic and lifestyle characteristics and selected NPC risk factors of the study population in Guangzhou, China

1 Continuous variables were shown as the means±standard deviation. Categorical variables were shown as numbers (percents). Variables were evaluated in conditional logistic model. 2 Variables were scored as yes or no, and numbers (percents) of yes responses were listed. House decoration refers to replacement of floor board, wall, and indoor painting for almost a whole flat or house; new furniture refers to a set of new furniture for living room(s) and bed room(s). 3 Occupation was categorized into 3 levels on the basis of the intensity of occupational physical activity. 4 Smoking status was defined as current smoker, ex-smoker or nonsmoker (a smoker was defined as someone smoking at least one cigarette per day for at least six months). 5 Passive smoking was designated as exposure to other peoples' tobacco smoke for at least 5 minutes daily in the previous five years. 6 Physical activity was defined as occupational, leisure time and household chores activity, and evaluated by metabolic equivalent hours per day (MET∙ h/d). Abbreviations: BMI: body mass index; NPC: Nasopharyngeal carcinoma; MET: metabolic equivalent 1 .