Assessment of bias
| Type of bias | Zhu et al.21 | Schunmann and Glasier19 | Nobili et al.17 | Langston et al.22 | Carneiro Gomes Ferreira et al.18 | Bender and Griersson20 |
|---|---|---|---|---|---|---|
| Random sequence generation (selection bias) | + | – | – | + | + | + |
| Allocation concealment (selection bias) | ? | – | – | + | ? | ? |
| Blinding of participants and study personnel (performance bias) | – | – | ? | + | ? | ? |
| Blinding of outcome assessment (detection bias) | – | ? | – | – | ? | ? |
| Incomplete outcome data (attrition bias) | + | + | + | + | ? | – |
| Selective reporting (reporting bias) | ? | ? | ? | + | ? | ? |
| Other bias | + | + | – | ? | – | – |
Key: +, low risk of bias; −, high risk of bias; ?, unclear risk of bias.