Quality assessment of included studies
| First author | Internal validity (Cochrane’s collaboration tool for assessing risk of bias) | External Validity | Precision | Overall quality | ||||||
| Selection bias | Performance bias | Detection bias | Attrition bias | Reporting bias | Other | |||||
| Random sequence generation | Allocation concealment | Blinding of patients and staff | Blinding of outcome measures | Completeness of outcome data | Selective reporting | |||||
| Brox36 | Low | ? | High | Low | Low | High | Low | Low | Low | Moderate |
| Rahme37 | Low | ? | High | Low | High | High | High | High | Low | Poor |
| Rompe30 | High | ? | High | High | Low | Low | Low | Low | ? | Poor |
| Keizer32 | ? | ? | High | High | Low | High | High | Low | High | Poor |
| Haahr35 | Low | Low | High | High | Low | Low | Low | Low | Low | Moderate |
| Bahr27 | Low | Low | High | High | Low | Low | Low | Low | Low | Moderate |
| Alfredson33 | Low | Low | High | High | Low | High | High | High | High | Poor |
| Radwan31 | ? | Low | High | High | Low | Low | ? | Low | Low | Moderate |
| Ketola29 | Low | Low | High | Low | Low | High | ? | High | Low | Poor |
| Farfaras28 | Low | ? | High | Low | High | Low | Low | Low | High | Poor |
| Beard34 | Low | Low | Low High | Low | Low | Low | Low | Low | Low | Good |
| Kroslak22 | Low | Low | Low | Low | Low | Low | Low | Low | High | Good |