Assessment of internal validity, external validity, precision and overall quality of each study (see table 1 for criteria for overall study quality assessment)
| 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 | |||||
| Berrazueta et al 13 | ? | ? | ? | Low | Low | High | High | Low | High | Poor |
| Pons et al 32 | Low | ? | High | High | Low | High | High | High | High | Poor |
| Steunebrink et al 35 | Low | Low | ? | ? | Low | High | High | Low | Low | Moderate |
| Giner-Pascual et al 33 | Low | Low | ? | ? | High | High | High | High | High | Poor |
| Paoloni et al 29 | ? | Low | Low | Low | Low | High | Low | Low | Low | Good |
| Kane et al 30 | ? | ? | High | ? | Low | High | High | Low | High | Poor |
| Paoloni et al 28 | ? | Low | Low | Low | Low | Low | Low | Low | Low | Good |
| Ozden et al 34 | ? | ? | ? | Low | Low | High | Low | Low | Low | Good |
| Paoloni et al | Low | ? | Low | Low | Low | High | High | Low | Low | Moderate |
| Paoloni et al 27 | ? | Low | ? | Low | Low | High | ? | Low | Low | Good |
?, unclear risk of bias.