Table 1

Demographic characteristics of participants included in the analysis

NSevere COPD (%)**Moderate COPD (%)Mild COPD (%)Symptoms only (%)Restrictive disease (%)Death
Participants included in the analysis were stratified by age, race, sex, education level, and smoking status at the baseline evaluation; the age adjusted* proportion within each subgroup with class of COPD, respiratory symptoms, or restrictive lung disease; and the age adjusted proportion who died during the follow up period.
*Age adjusted to the analytical population sample. Proportions by age are age specific.
**Severe COPD = forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) <0.70 and FEV1 <50% predicted; moderate COPD=FEV1/FVC <0.70 and FEV1 ⩾50–<80% predicted; mild COPD=FEV1/FVC <0.70 and FEV1 ⩾80%; symptoms only=presence of respiratory symptoms in the absence of any lung function abnormality; restrictive lung disease=FEV1/FVC ⩾0.70 and FVC <80% predicted.
From the First National Health and Nutrition Examination Survey 1971–5 and follow up to 1992.
    ⩽12 years40441.97.68.316.69.024.2
    ⩾13 years14980.95.26.814.810.121.0
Smoking status
    Current smoker23232.511.810.320.210.030.2
    Former smoker11101.86.67.915.96.922.0
    Never smoker21090.92.85.910.59.417.9
Pack years
     Never smoker21090.92.85.910.59.417.9
Years since regularly smoked
    Never smoker21090.92.85.910.59.417.9
Body mass index (kg/m2)