Data are presented as %, unless otherwise stated. The low risk for dyspnoea subgroup of study participants was defined as those without post-pronchodilator (BD) airflow restriction, spirometric chronic obstructive pulmonary disease (COPD) or pre-BD airflow obstruction, or self-reported heart disease, asthma, attacks of wheezing and dyspnoea, emphysema, chronic bronchitis, COPD, tuberculosis or lung cancer.