Effect modification between smoking or opium consumption and employment as a construction worker among men
| Exposure status | N Case/Controls | OR (95% CI) |
| Never smoker and never construction worker | 235/2304 | Ref |
| Never smoker and construction worker | 14/174 | 1.1 (0.6 to 2.1) |
| Ever smoker and never construction worker | 328/855 | 3.4 (2.6 to 4.5) |
| Ever smoker and ever construction worker | 81/141 | 4.8 (3.2 to 6.7) |
| P value multiplicative interaction | 0.1 | |
| RERI* | 1.2 (–0.4 to 2.8) | |
| Never opium user and never construction worker | 313/2786 | Ref |
| Never opium user and construction worker | 33/240 | 1.3 (0.8 to 2.0) |
| Ever opium user and never construction worker | 250/373 | 4.7 (3.6 to 6.1) |
| Ever opium user and ever construction worker | 62/78 | 6.4 (4.2 to 9.6) |
| P value multiplicative interaction | 0.3 | |
| RERI† | 1.4 (–1.1 to 3.9) |
*Adjusted OR for age categories (5-year categories) and residence (provinces).
†Interaction on an additive scale.
N, number; RERI, relative excess risk due to interaction.