TABLE 1.
Characteristics of the study population
| All subjects | No incident COPD events # | Incident COPD events # | p-value for no COPD – COPD difference | ||||
| Subjects n | 615 | 561 | 54 | ||||
| Person-years of observation | 13 553 | 12 717 | 836 | ||||
| Age at baseline (years) | 625 | 56.8±4.8 | 571 | 56.8±4.7 | 54 | 56.4±4.9 | 0.53 |
| BMI (kg·m−2) | 625 | 25.6±3.3 | 571 | 25.6±3.2 | 54 | 25.2±3.5 | 0.34 |
| FEV1 (% pred) ¶ | 615 | 88.7±16.4 | 561 | 90.2±15.0 | 54 | 72.2±20.9 | <0.0001 |
| FEV1/VC (% pred) ¶ | 615 | 99.6±11.4 | 561 | 100.0±9.8 | 54 | 87.0±17.8 | <0.0001 |
| N2-slope (% N2/L) + | 604 | 2.0±1.5 | 552 | 1.9±1.4 | 52 | 3.1±2.1 | <0.0001 |
| N2-slope (% pred) + | 604 | 162±118 | 552 | 154±110 | 52 | 253±155 | <0.0001 |
| Smoking habits | 625 | <0.0001 | |||||
| Never-smoker (%) | 125 | 20.0 | 121 | 21.2 | 4 | 7.4 | |
| Ex-smoker (%) | 194 | 31.0 | 181 | 31.4 | 13 | 24.1 | |
| Current smoker (%) | 306 | 49.0 | 269 | 47.1 | 37 | 68.5 | |
| Non-productive cough (%) § | 149 | 24.1 | 124 | 21.9 | 25 | 47.2 | <0.0001 |
| Productive cough (%) § | 139 | 22.5 | 115 | 20.3 | 24 | 45.3 | <0.0001 |
| Wheezing (%) § | 219 | 35.4 | 186 | 32.9 | 33 | 62.3 | <0.0001 |
| Dyspnoea (%) § | 160 | 26.0 | 131 | 23.3 | 29 | 54.7 | <0.0001 |
| Total symptom score ƒ | 619 | 2.0±2.6 | 556 | 1.8±2.4 | 53 | 4.4±3.2 | <0.0001 |
Data are presented as n or mean±sd, unless otherwise stated. Continuous variable differences were tested using the Mann–Whitney U-test; discrete variables were tested using the Chi-squared test. BMI: body mass index; FEV1: forced expiratory volume in 1 s; VC: vital capacity; N2-slope: alveolar slope of the single-breath nitrogen test. #: first admission to hospital or death related to COPD; ¶: according to Hedenström et al. [16]; +: according to Sixt et al. [17]; §: percentage of subjects reporting any of the symptoms in each symptom group; ƒ: mean of all the reported symptoms.