Table 3 Distribution of the main characteristics of the 218 studies of COPD, CB and/or emphysema
| Â | Â | Disease studied (principal studies) | Study type (principal studies)a | Subsidiary | All | ||||
|---|---|---|---|---|---|---|---|---|---|
Characteristic | Level | COPD | CB | EMP | CC | Prosp | Cross-sec | studies | studies |
Study status | Principal | 116 | 87 | 26 | 20 | 39 | 134 | - | 193 |
| Â | Subsidiary | (17) | (14) | (2) | - | - | - | 25 | 25 |
Study type | Case/control | 14 | 7 | 0 | 20 | - | - | 2 | 22 |
| Â | Prospective | 35 | 9 | 7 | - | 39 | - | 8 | 47 |
| Â | Cross-sectional | 67 | 71 | 19 | - | - | 134 | 14 | 148 |
| Â | Nested case/control | 0 | 0 | 0 | - | - | - | 1 | 1 |
Study sex | Both | 89 | 62 | 18 | 17 | 20 | 108 | 20 | 165 |
| Â | Male | 23 | 20 | 8 | 2 | 17 | 23 | 5 | 47 |
| Â | Female | 4 | 5 | 0 | 1 | 2 | 3 | 0 | 6 |
Lowest ageb | < 20 | 26 | 22 | 10 | 5 | 4 | 42 | 3 | 54 |
| Â | 20-29 | 28 | 25 | 2 | 3 | 10 | 32 | 9 | 54 |
| Â | 30-39 | 23 | 12 | 4 | 6 | 15 | 11 | 6 | 38 |
| Â | 40-49 | 26 | 17 | 4 | 5 | 7 | 29 | 5 | 46 |
| Â | 50+ | 13 | 11 | 6 | 1 | 3 | 20 | 2 | 26 |
Highest ageb | < 50 | 3 | 6 | 0 | 0 | 2 | 6 | 1 | 9 |
| Â | 50-59 | 4 | 8 | 0 | 0 | 4 | 8 | 1 | 13 |
| Â | 60-69 | 20 | 21 | 6 | 2 | 9 | 29 | 5 | 45 |
| Â | 70-79 | 19 | 12 | 1 | 4 | 6 | 19 | 8 | 37 |
| Â | 80+ | 70 | 39 | 19 | 14 | 18 | 71 | 10 | 113 |
| Â | Unknown | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 1 |
Region | USA/Canada | 31 | 28 | 12 | 2 | 14 | 40 | 7 | 63 |
| Â | S/C America | 7 | 2 | 0 | 2 | 0 | 6 | 0 | 8 |
| Â | UK | 11 | 13 | 1 | 5 | 6 | 12 | 5 | 28 |
| Â | Western Europe | 8 | 9 | 1 | 4 | 2 | 11 | 1 | 18 |
| Â | Scandinavia | 18 | 16 | 5 | 0 | 6 | 26 | 7 | 39 |
| Â | Other Europe | 12 | 4 | 0 | 2 | 1 | 11 | 4 | 18 |
| Â | Asia | 22 | 10 | 6 | 4 | 7 | 21 | 1 | 33 |
| Â | Other | 3 | 4 | 1 | 1 | 1 | 5 | 0 | 7 |
| Â | Multicountry | 4 | 1 | 0 | 0 | 2 | 2 | 0 | 4 |
Start year of study | < 1960 | 7 | 10 | 3 | 2 | 7 | 4 | 3 | 16 |
| Â | 1960-1969 | 19 | 15 | 4 | 1 | 12 | 17 | 8 | 38 |
| Â | 1970-79 | 15 | 19 | 5 | 1 | 9 | 23 | 6 | 39 |
| Â | 1980-89 | 12 | 10 | 4 | 2 | 5 | 13 | 2 | 22 |
| Â | 1990-99 | 23 | 16 | 6 | 2 | 6 | 29 | 3 | 40 |
| Â | > 1999 | 25 | 1 | 0 | 2 | 0 | 24 | 1 | 27 |
| Â | Unknown | 15 | 16 | 4 | 10 | 0 | 24 | 2 | 36 |
Major study weakness | Present | 19 | 5 | 2 | 9 | 4 | 13 | 6 | 32 |
Smoking results available | Current v never | 89 | 70 | 15 | 14 | 34 | 98 | 23 | 169 |
| Â | Ex v never | 82 | 65 | 12 | 12 | 29 | 93 | 19 | 153 |
| Â | Ever v never | 95 | 71 | 20 | 16 | 29 | 113 | 18 | 176 |
| Â | Amount smoked | 39 | 42 | 10 | 7 | 23 | 47 | 14 | 91 |
| Â | Age started | 13 | 3 | 1 | 5 | 7 | 5 | 3 | 20 |
| Â | Pack years | 42 | 13 | 3 | 10 | 5 | 43 | 5 | 63 |
| Â | Duration of smoking | 6 | 4 | 3 | 2 | 4 | 6 | 2 | 14 |
| Â | Duration of quitting | 8 | 7 | 2 | 3 | 8 | 7 | 4 | 22 |
Outcomes | COPD only | 93 | - | - | 13 | 28 | 52 | 11 | 104 |
| Â | CB only | - | 63 | - | 6 | 2 | 55 | 7 | 70 |
| Â | Emp only | - | - | 9 | 0 | 1 | 8 | 0 | 9 |
| Â | More than one | 23 | 24 | 17 | 1 | 8 | 19 | 7 | 35 |
| Â | COPD | 116 | - | - | 14 | 35 | 67 | 17 | 133 |
| Â | CB | - | 87 | - | 7 | 9 | 71 | 14 | 101 |
| Â | Emp | - | - | 26 | 0 | 7 | 19 | 2 | 28 |
All studies | Â | 116 | 87 | 26 | 20 | 39 | 134 | 25 | 218 |