Table 1

Baseline characteristics according to change in severity of obstruction* during follow-up

Persistently normalIncident stage IIncident stage IIPersistent stage IStage I progressingPersistent stage IINon-persistent
n = 4181n = 683n = 85n = 294n = 56n = 61n = 113
Female sex (%)54.754.244.739.133.932.840.7
Age in years (mean/SD)39.2/11.245.3/10.344.5/11.948.8/9.648.5/9.249.5/9.147.0/9.1
No professional education (%)12.116.423.515.621.419.78.8
FEV1 % of predicted value (mean/SD)109.9/13.6107.4/12.591.3/12.5101.3/10.989.1/7.067.4/10.499.6/13.5
FVC % of predicted value (mean/SD)114.0/0.2119.2/0.1100.6/0.1125.9/0.1116.0/0.196.0/0.1122.4/0.2
FEV1/FVC % of predicted value (mean/SD)100.9/0.194.6/0.194.9/0.184.1/0.080.2/0.173.3/0.184.8/0.0
Never smoker (%)49.944.735.336.719.631.138.9
Light smoker at baseline (<15 pack-years)† (%)28.719.313.620.99.311.824.5
Heavy smoker at baseline (≥15 pack-years)† (%)18.231.842.438.462.552.529.2
Shortness of breath at baseline (%)21.725.042.425.544.647.514.2
Chronic bronchitis at baseline (%)7.311.620.013.319.627.99.7
Wheezing in last 12 months at baseline4.87.822.49.928.620.08.0
Non-current asthma at baseline (%)5.610.517.612.221.427.99.7
Current asthma at baseline (%)1.83.411.84.416.116.44.4
Health service use for respiratory problems at baseline (%)
  • * Obstruction was defined as FEV1/FVC <0.70 based on prebronchodilation spirometry.

  • Numbers do not add up to 100.0% due to smokers with missing pack-year information.

  • FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity.