Figure 1.

Flow diagram of participants included in the survey. ^aResponse rate. ^bActual response rate (participants included in the analysis and had completed all sections that comprised questionnaire, physical measurements and tests during the second resurvey). ^cChronic obstructive pulmonary disease (COPD) defined by history of doctor diagnosis of COPD=COPD and/or chronic bronchitis and/or emphysema. ^dSymptom-based COPD are those with self-reported chronic cough, that is, productive cough for at least 3 months for 2 consecutive years.