Table 1.
Base models explored as stepwise regressions and candidate items included in analysis
| Predictors of obstruction | |
|---|---|
| 1 | Age (50+ years), BMI (<18 kg/m2), cough, phlegm, dypsnea, wheeze1, smoke (≥20 years) |
| 2 | Age (60+ years), BMI (<18 kg/m2), cough, phlegm, dypsnea, wheeze1, smoke (≥20 years) |
| 3 | Age (50+ years), BMI (<25 kg/m2), cough, phlegm, dypsnea, wheeze1, smoke (≥20 years) |
| 4 | Age (60+ years), BMI (<25 kg/m2), cough, phlegm, dypsnea, wheeze1, smoke (≥20 years) |
| 5 | Age (50+ years), BMI (<18 kg/m2), cough, phlegm, dypsnea, wheeze2, smoke (≥20 years) |
| 6 | Age (60+ years), BMI (<18 kg/m2), cough, phlegm, dypsnea, wheeze2, smoke (≥20 years) |
| 7 | Age (50+ years), BMI (<25 kg/m2), cough, phlegm, dypsnea, wheeze2, smoke (≥20 years) |
| 8 | Age (60+ years), BMI (<25 kg/m2), cough, phlegm, dypsnea, wheeze1, smoke (≥20 years) |
Notes: Age was a categorical variable, and different age cutoffs were explored. An age cutoff of 50 years and older was the most predictive category. Therefore, the age variable in this analysis was age 50 years (Yes/No). Body mass index (BMI) was a continuous variable, and two cutoffs were explored (<18 kg/m2 and <25 kg/m2); Cough was defined in NHANES as “Do you usually cough on most days for three consecutive months or more during the year?” (Yes/No). Wheeze1 was defined in NHANES as “Have you had wheezing or whistling in your chest at any time in the past 12 months?” (Yes/No). Wheeze2 was defined in NHANES as “Apart from when you have a cold, does your chest ever sound wheezy or whistling?” (Yes/No). Dyspnea was originally captured in NHANES as “Are you troubled by shortness of breath when hurrying on level ground or walking up a slight hill?” (Yes/No). Phlegm was originally defined in NHANES as “Do you bring up phlegm on most days for three consecutive months or more during the year?” (Yes/No). Smoke was defined in NHANES as “For approximately how many years have you smoked this amount?” (a question was preceded by “About how many cigarettes do you smoke per day”). For the purposes of this analysis, smoking for 20 years was used as the frame of reference for the question.