Ulcer perforation and increasing levels of cigarette smoking in the age group 15–74 years in western Norway. The odds ratios are adjusted for age and sex by multiple logistic regression analyses
| Patients | Controls | Odds ratio (95% CI) | |
| Never smoked | 14 (13%) | 1819 (42%) | 1 |
| Ex smokers | 8 (7%) | 882 (21%) | 0.8 (0.2–2.2) |
| 1–9 cigarettes daily | 17 (16%) | 321 (7%) | 7.3 (4.0–18.1) |
| 10–19 cigarettes daily | 44 (40%) | 880 (21%) | 8.7 (5.5–14.4) |
| ⩾20 cigarettes daily | 26 (24%) | 368 (9%) | 11.2 (6.3–27.5) |
| Total | 109 (100%) | 4270 (100%) |