| First author [ref.] | Patients n | Age yrs | Males n (%) | Definition of COPD | FEV1 % pred |
| Wagena [25] | I1: 86 I2: 80 C: 89 | I1: 51.1±8.3 I2: 51.2±9.1 C: 51.3±8.4 | I1: 34 (40) I2: 44 (55) C: 46 (52) | GOLD criteria, stage 0 (at risk for) included [46] | I1: 86.3±21.0 I2: 83.1±21.7 C: 87.4±23.0 |
| Tønnesen [9] | I1: 95 I2: 90 I3: 97 C: 88 | I1: 59.2±10.3 I2: 61.3±9.6 I3: 61.2±9.4 C: 62.5±9.3 | I1: 45 (47) I2: 46 (51) I3: 46 (47) C: 40 (46) | Post-bronchodilator FEV1/FVC <70% FEV1 <90% pred | I1: 55.1±15.4 I2: 53.4±19.4 I3: 58.2±17.8 C: 56.0±19.1 |
| Christenhusz [43, 44] | I: 114 C: 111 | I: 57.0±8.4 C: 59.6±8.5 | I: 55 (48) C: 63 (57) | FEV1 <69% pred# | I: 65.6±27.4 C: 62.8±25.7 |
| Wilson [37] | I1: 27 I2: 29 C: 35 | I1: 61.0±8 I2: 60.4±9 C: 61.4±8 | I1: 14 (52) I2: 12 (41) C: 18 (51) | FEV1/FVC <70% FEV1 <80% pred¶ | I1: 52.1±20 I2: 54.6±23 C: 54.3±20 |
| Borglykke [45] | I: 121 C: 102 | I: 65 C: 67 | I: 42 (35) C: 37 (36) | Patients having symptoms of COPD | Not available |
| Kotz [39] | I1: 116 I2: 112 C: 68 | I1: 53.8±7.0 I2: 54.9±8.0 C: 53.0±7.6 | I1: 71 (61) I2: 74 (66) C: 40 (59) | Post-bronchodilator FEV1/FVC <70% FEV1 ≥50% pred | I1: 80.5±14.7 I2: 83.7±16.8 C: 79.7±14.0 |
| Tashkin [38] | I: 248 C: 251 | I: 57.2±9.1 C: 57.1±9.0 | I: 155 (63) C: 156 (62) | Post-bronchodilator FEV1/FVC <70% FEV1 ≥50% pred | I: 70.8±17.0 C 69.1±16.9 |
| Hilberink [41, 42] | I1: 243 I2: 276 C: 148 | I1: 58.0±12.2 I2: 60.7±11.2 C: 60.1±11.5 | I1: 113 (47) I2: 132 (48) C: 82 (55) | Clinical criteria by GP | Not available |
Data are presented as mean±sd, unless otherwise stated. COPD: chronic obstructive pulmonary disease; FEV1: forced expiratory volume in 1 s; % pred: % predicted; I: intervention group; C: control group; GOLD: Global Initiative for Chronic Obstructive Lung Disease; FVC: forced vital capacity; GP: general practitioner. #: moderate or severe COPD according to American Thoracic Society criteria [47]; ¶: COPD according to National Institute for Health and Clinical Excellence guidelines [48].