Assessment of methodological quality for each study
| Risk of bias domain | Gabbe et al 16 | Brooks et al 33 | Arnason et al 34 | Soligard et al 35 | Engebretsen et al 17 | Petersen et al 9 | Owen et al 36 | Grooms et al 37 | Sebelien et al 38 | Seagrave et al 39 | Van der Horst et al 10 | Silvers-Granelli et al 40 | del Ama Espinosa et al 41 | Nouni Garcia et al 42 | González43 |
| Random sequence generation (selection bias) | − | + | + | − | − | − | + | + | − | + | − | − | − | + | + |
| Allocation concealment (selection bias) | − | + | + | − | − | − | + | + | − | + | − | − | − | + | + |
| Blinding of participants and personnel (performance bias) | + | + | + | + | + | + | + | + | + | + | + | − | + | + | + |
| Blinding of outcome assessment (detection bias) | + | + | + | − | + | + | + | + | + | + | + | − | + | + | + |
| Incomplete outcome data (attrition bias) | − | − | − | − | − | − | ? | − | + | − | − | − | − | − | − |
| Selective reporting (reporting bias) | − | − | ? | − | − | − | − | − | − | − | − | − | − | − | − |
| Other bias | − | − | − | − | − | − | − | − | − | − | − | − | − | − | ? |
Positive signs indicate a high risk of bias, negative signs indicate a low risk of bias and question marks indicate an unknown risk of bias.