The FEV1 was classified as mild, moderate, severe, or very severe (corresponding to a score of 1, 2, 3, or 4) based on the following prebronchodilator cutpoints: > 80%, > 50% to 80%, > 30% to 50%, and ≤ 30%. Smoking category was determined using the validated status at years 1 and 2 and classified as current, former, or intermittent smokers (the final category comprised subjects for whom the status changed between visits 1 and 2). Symptoms were counted with response to the following questions: “Do you usually have a cough?”, “Do you usually bring up phlegm from your chest?”, “Does your chest ever sound wheezy or whistling (occasionally, apart from colds)?”, and “Are you troubled by shortness of breath when hurrying on the level or walking up a slight hill?” Each positive response counted as one symptom and severity was graded as 0, 1, 2, or 3 or more symptoms. Exacerbations were assessed using the question “How often did you get colds in the past year?”, with possible responses being Not at all, once, 2-4, and 5 or more. These categories were used to classify exacerbation severity. Comorbidity was assessed by adding up the new diagnoses since the previous visit of lung cancer, breast cancer, other cancer, heart attack, congestive heart failure, hypertension, stroke, diabetes. Each of these counted as one point, and subjects were graded as 0, 1, 2, or 3 or more comorbidities. For year 5, data from all of the intervening years were used. Subjects were supposed to be free of comorbid disease at the baseline examination. BMI was assessed and classified as ≤ 20 kg/m3, > 20 to < 25 kg/m3, and ≥ 25 kg/m3.