2.4. Data collection
2.4.1. General information
Questionnaires were administered by the trained interviewers to all partici- pants during each interview. Two different questionnaires were designed for the baseline and follow-up interviews, respectively. The baseline questionnaire included questions regarding residential address, tobacco use, alcohol use, tea drinking, dietary habits, occupational history, medical history, frequency of stir/ deep frying food per day and usage of ventilation in their kitchen, recent incidence of cold and other respiratory diseases, and recent subjective feeling about outdoor air pollution and related symptoms. The follow-up questionnaire focused on questions regarding subjects’ change in residential location, lifestyle, occupation, physical condition, and disease symptoms since the previous interview.