Table 2 Characteristics of the study population
Screened subjects
Without baseline abnormalities (n = 151)With baseline abnormalities (n = 313)
Year 0Year 5Year 0Year 5
Age42.9 (11.2)48.0 (11.2)44.0 (11.5)49.2 (11.5)
Gender (% female)50.350.359.459.4
FEV1* (ml)3532 (833)3335 (806)3195 (795)2938 (802)
FEV1/VC (%)84.5 (8.3)79.3 (7.9)81.3 (9.8)73.0 (8.8)
Screening criteria†
    Respiratory symptoms‡37.188.880.5
    Lung function <normal range§4.616.620.8
    Reversibility¶0.72.92.9
    Mild early signs**9.331.632.6
Mucus hypersecretion††0.74.614.413.7
Pack-years8.9 (12.0)8.7 (10.8)
Ever smokers (%)43.143.732.634.2
Current smokers (%)31.827.240.636.7
  • Values are mean (SD).

  • *Post-bronchodilator FEV1 (at 5 years: n = 150 and n = 299, respectively).

  • †Screening criteria, used to determine the respiratory status of subjects (see table A1 in appendix 1).

  • ‡Dutch modified version of the Medical Research Council questionnaire.

  • §FEV1/VC ⩽ lower limit of normal.

  • ¶⩾15% predicted.

  • **Combination of at least two out of three mild early signs (mild obstruction or reversibility, or a weather dependent cough or shortness of breath, or a recurrent productive cough).

  • ††Continuous production of sputum in the winter season.

  • COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 s; VC, vital capacity.