Respiratory symptoms in daily smokers, by number of cigarettes smoked per day
| Cigarettes per day | Chi-squared | p-value | ||||
| 1–9 | 10–19 | 20–24 | ≥25 | |||
| Subjects n | 1432 | 4056 | 2750 | 2236 | ||
| Median age yrs | 30.0 | 31.5 | 35.0 | 40.0 | 639.7 | <0.001 |
| Males % | 41.7 | 41.9 | 49.0 | 54.1 | 109.1 | <0.001 |
| Do you often cough even without a cold? % | 28.8 | 40.4 | 48.8 | 62.0 | 462.7 | <0.001 |
| Do you expectorate when you cough in the morning? % | 30.3 | 41.1 | 50.2 | 57.9 | 329.4 | <0.001 |
| Are you out of breath after an effort like climbing stairs or a quick walk? % | 57.8 | 72.1 | 77.9 | 82.6 | 311.0 | <0.001 |
| Do you have a wheezing respiration? % | 23.7 | 28.9 | 36.9 | 47.1 | 294.5 | <0.001 |
| None of the above four symptoms % | 22.8 | 11.3 | 7.6 | 4.2 | 921.1 | <0.001 |