| Characteristic | COPD(n = 1202) | Referents(n = 302) | p Value |
| Mean (SD) age (years) | 58.2 (6.2) | 58.5 (6.2) | 0.50 |
| Female, n (%) | 691 (57.4%) | 185 (61%) | 0.23 |
| Race/ethnicity, n (%) | 0.96 | ||
| White, non-Hispanic | 810 (67%) | 200 (66%) | |
| African-American | 206 (17%) | 57 (19%) | |
| Asian/Pacific Islander | 35 (3%) | 8 (3%) | |
| Hispanic | 111 (9%) | 28 (9%) | |
| Other | 40 (3%) | 9 (3%) | |
| Educational attainment, n (%) | <0.0001 | ||
| High school or less | 352 (29%) | 42 (14%) | |
| Some college | 524 (44%) | 95 (31%) | |
| College/graduate degree | 326 (27%) | 165 (55%) | |
| Household income,* n (%) | <0.0001 | ||
| Low (<$20 000) | 129 (11%) | 9 (3%) | |
| $20 000–80 000 | 699 (58%) | 137 (45%) | |
| High (>$80 000) | 276 (23%) | 133 (44%) | |
| Smoking status, n (%) | <0.0001 | ||
| Never smoked | 165 (13%) | 158 (52%) | |
| Current smoker | 393 (33%) | 12 (4%) | |
| Ex-smoker | 644 (54%) | 132 (44%) | |
| Smoking, n (%) | <0.001 | ||
| None | 162 (13%) | 158 (52%) | |
| <20 pack-years | 627 (52%) | 92 (30%) | 0.43† |
| ⩾20 pack-years | 410 (34%) | 52 (17%) |
*98 (8%) of the COPD group and 23 (8%) of the referent group declined to state income.
†Comparing proportions of <20 vs ⩾20 pack-years among ever smokers only.