Level of evidence of the research studies
| Level of evidence | Number of studies | Percent of total | Mean number of centers (SD) | Mean number of authors (SD) |
|---|---|---|---|---|
| 1 | 3 | 1.5 | 4.0 (2.0) | 6.0 (1.7) |
| 2 | 7 | 3.4 | 4.6 (3.8) | 8.6 (4.0) |
| 3 | 9 | 4.4 | 2.0 (0.9) | 6.0 (2.5) |
| 4 | 97 | 47.1 | 2.2 (1.6) | 7.8 (2.8) |
| 5 | 90 | 43.7 | 1.7 (1.1) | 5.5 (2.5) |
| Total | 206 | 100 | 2.1 (1.6) | 6.8 (2.9) |