Characteristics of the study population

All subjectsNo incident COPD events#Incident COPD events#p-value for no COPD – COPD difference
Subjects n61556154
Person-years of observation13 55312 717836
Age at baseline (years)62556.8±4.857156.8±4.75456.4±4.90.53
BMI (kg·m−2)62525.6±3.357125.6±3.25425.2±3.50.34
FEV1 (% pred)61588.7±16.456190.2±15.05472.2±20.9<0.0001
FEV1/VC (% pred)61599.6±11.4561100.0±9.85487.0±17.8<0.0001
N2-slope (% N2/L)+6042.0±1.55521.9±1.4523.1±2.1<0.0001
N2-slope (% pred)+604162±118552154±11052253±155<0.0001
Smoking habits625<0.0001
 Never-smoker (%)12520.012121.247.4
 Ex-smoker (%)19431.018131.41324.1
 Current smoker (%)30649.026947.13768.5
Non-productive cough (%)§14924.112421.92547.2<0.0001
Productive cough (%)§13922.511520.32445.3<0.0001
Wheezing (%)§21935.418632.93362.3<0.0001
Dyspnoea (%)§16026.013123.32954.7<0.0001
Total symptom scoreƒ6192.0±2.65561.8±2.4534.4±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.