Expected and observed number of cases of obstructive pulmonary function test patterns among all employees categorised by smoking status and age
| Age | Total | ||
| ≤39 yrs | ≥40 yrs | ||
| Current or former smokers | |||
| Subjects n | 209 | 225 | 434 |
| Expected | 8.05 | 27 | 34.6 |
| Observed | 7 | 30 | 37 |
| Prevalence ratio | 0.87 | 1.11 | 1.07 |
| Never-smokers | |||
| Subjects n | 144 | 179 | 323 |
| Expected | 3.33 | 4.82 | 7.46 |
| Observed | 6 | 3 | 9 |
| Prevalence ratio | 1.80 | 0.62 | 1.21 |
| All | |||
| Subjects n | 353 | 404 | 757 |
| Expected | 10.87 | 34.06 | 41.8 |
| Observed | 13 | 33 | 46 |
| Prevalence ratio | 1.20 | 0.97 | 1.10 |
Expected values obtained from the third National Health and Nutrition Examination Survey and calculated by Kreiss et al. 7. Includes all employees with valid tests (n = 757), including 11 office workers and 21 employees reporting asthma prior to employment who were excluded from the primary analyses. All prevalence ratios were nonsignificant (p>0.05).