| Variable | Prospective cohort | Retrospective cohort | p-value |
| Subjects n | 70 | 68 | |
| M/F (% male) | 57/13 (81) | 50/18 (74) | ns |
| Age yrs | 67±8 | 62±9 | 0.0011 |
| BMI m·kg−2 | 28±4 | 27±5 | ns |
| Time to diagnosis months | 23±20 | NA | NA |
| Biopsy-based diagnosis yes/no (%) | 23/47 (33) | 22/46 (32) | ns |
| Smokers/never-smokers (%) | 44/26 (63) | 34/34 (50) | ns |
| Smoking pack-yrs | 33±18 | 24±17 | 0.028 |
| Concomitant emphysema yes/no (%) | 24/46 (34) | 13/55 (19) | 0.044 |
| MRC dyspnoea score | 2.5±1.1 | NA | NA |
| 6MWD¶ m | 372±146 | 350±116 | ns |
| 6MWD¶ % pred | 79±29 | 68±24 | 0.049 |
| PA–a,O2 mmHg | 32±14 | 26±10 | ns |
| FVC % pred | 75±22 | 75±21 | ns |
| DL,CO+ % pred | 46±19 | 55±17 | 0.013 |
| CPI | 48±15 | 42±12 | 0.038 |
| HRCT disease extent§ % of total lung volume | 36±12 | NA | NA |
| BAL total cell countƒ cells·mL−1 | 596130±502073 | NA | NA |
Data are presented as mean±sd, unless otherwise stated. M: male; F: female; BMI: body mass index; MRC: Medical Research Council; 6MWD: 6-min walking distance; % pred: % predicted; PA–a,O2: alveolar–arterial oxygen tension difference; FVC: forced vital capacity; DL,CO: diffusing capacity of the lung for carbon monoxide; CPI: composite physiologic index; HRCT: high-resolution computed tomography; BAL: bronchoalveolar lavage; ns: not significant; NA: not available. #: a prospective cohort at the Pulmonary Unit, University of Rome “Tor Vergata”, Rome, Italy and a retrospective cohort at the pulmonary unit, University of Siena, Siena, Italy; ¶: n=64; +: n=65; §: mean of the scores from each of the three core radiologists; ƒ: n=28. p-value: Chi-squared, unpaired t-test or Mann–Whitney U-test, where required.