Association between chronic bronchitis and relevant occupational long term exposure (>5 y) to physical and chemical factors
| Exposure | Chronic bronchitis n=485 (%) | No bronchitis n=2846 (%) | p Value |
| Cold and draught | 60 | 49 | <0.001 |
| Strong variations of temperature | 40 | 31 | <0.001 |
| Strong heat | 15 | 11 | 0.024 |
| Moist and humidity | 14 | 10 | 0.010 |
| Dust (concrete, granite, etc) | 13 | 8 | <0.001 |
| Asbestos | 7 | 4 | 0.004 |
| Soldering fumes | 10 | 9 | 0.447 |
| Welding fumes | 13 | 9 | 0.020 |
| Organic solvents | 16 | 10 | <0.001 |
| Vapours from lacquer, paint, varnish | 8 | 6 | 0.125 |
| Plastic (manufacture of or exposure to vapours) | 2.7 | 1.1 | 0.011 |
| Glass fibre | 2.5 | 1.6 | 0.145 |
p Values are of Yates's corrected χ2 tests. Variables are presented according to their order in the questionnaire.