Chronic obstructive pulmonary disease (COPD) was defined as a spirometric result for forced expiratory volume in 1 second/forced vital capacity of <0.7 in adults aged >40 years. A history of asthma, tuberculosis, hypertension, diabetes, hyperlipidemia, and/or cardiac disease was obtained by a self-administered questionnaire asking “Have you been diagnosed with the disease by a doctor?” or “Do you take medicine or treatment for the disease?” Since, many Koreans with COPD are misdiagnosed as having asthma, asthma was only diagnosed if the subject reported a history of asthma but did not meet the criteria for COPD.