| Characteristics | Seen at phase 1 and 3 | Seen at phase 1 and 2 but not 3 | Seen at phase 1 only |
| Number (%) | Number (%) | Number (%) | |
| Smoking status* | |||
| Regular smoker | 83 (44) | 32 (36) | 43 (47) |
| Occasional smoker | 20 (10) | 12 (13) | 11 (12) |
| Ex-smoker | 30 (16) | 17 (19) | 11 (12) |
| Non-smoker | 56 (29) | 28 (31) | 26 (29) |
| Not answered | 2 (1) | 0 (0) | 0 (0) |
| Number (range) | Number (range) | Number (range) | |
| Cotinine levels (ng/ml) | |||
| Regular smoker | 284 (4.9–684) | 295 (84–827) | 274 (60–796) |
| Occasional smoker | 63 (0.6–167) | 55 (1.9–202) | 48 (13–90) |
| Ex-smoker | 17 (0.3–324) | 4.6 (0.4–244) | 74 (0.2–455) |
| Non-smoker | 3.3 (0.2–13.9) | 5.9 (0.5–36) | 6.7 (0.6–26) |
| Total | 191 | 89 | 91 |
*Smoking status here is based on self-report at phase 1. Our classification of smoking status for the analysis of symptoms further validates this self-report by salivary cotinine level.