| Centre | |||||
| C1 | C2 | C3 | C4 | C5 | |
| Subjects n (% male) | 66 (52) | 61 (46) | 71 (49) | 108 (50) | 62 (47) |
| Age years | 47.9±17.3 | 42.6±15.2* | 49.1±17.4 | 54.8±15.7* | 49.5±17.3 |
| Height cm | 171.8±9.9 | 174.7±9.0* | 170.3±10.8 | 170.5±9.8 | 170.8±9.2 |
| BMI kg·m−2 | 26.3±4.2 | 24.0±3.1* | 25.4±4.2 | 26.5±4.6 | 25.5±3.6 |
| FEV1 L | 3.6±1.0 | 3.8±0.9# | 3.4±0.9 | 3.1±0.9* | 3.4±0.9 |
| FEV1 % pred | 105±13 | 102±12 | 102±12 | 95±13*** | 104±13 |
| FEV1 z-score | 0.39±0.95 | 0.15±0.93 | 0.17±0.90 | -0.33±0.88*** | 0.30±0.93 |
| VC L | 4.4±1.2 | 4.7±1.1# | 4.2±1.2 | 3.9±1.1* | 4.4±1.1 |
| VC % pred | 104±12 | 103±10 | 101±12 | 95±12*** | 107±12# |
| VC z-score | 0.25±0.87 | 0.19±0.77 | 0.04±0.88 | -0.36±0.82*** | 0.43±0.83# |
| FEV1/VC % | 81±5 | 80±7 | 82±6 | 79±6¶ | 78±6+ |
| FEV1/VC z-score | 0.16±0.72 | -0.08±1.07 | 0.17±0.83 | 0.00±0.78 | -0.28±0.74§ |
Data are presented as mean±sd, unless otherwise stated. The Global Lungs Initiative reference equations [13] were used to express the spirometry data as percentages of those predicted (% pred) and as z-scores. C1: Antwerp, Belgium; C2: Enschede, the Netherlands; C3: Szeged, Hungary; C4: Perth, Australia; C5: Maastricht, the Netherlands; BMI: body mass index; FEV1: forced expiratory volume in 1 s; VC: vital capacity. *: p<0.05; ***: p<0.001 versus all the other centres; #: p<0.01 versus the data from C3; ¶: p<0.05 versus the data from C1 and C3; +: p<0.05 versus the data from C1, C2 and C3; §: p<0.05 versus the data from C1, C3 and C4.