Table 3.
Assessment of risk of bias of the selected studies.
| Studies | Selection bias | Performance bias | Detection bias | Attrition bias | Reporting bias |
| Alnosayan [31] | 3a | 3 | 2b | 2 | 1c |
| Athilingam [32] | 2 | 3 | 2 | 3 | 2 |
| Austin [41] | 3 | 3 | 2 | 3 | 2 |
| Bartlett [33] | 3 | 3 | 2 | 2 | 2 |
| Dang [42] | 2 | 2 | 3 | 2 | 2 |
| Evans [43] | 3 | 3 | 2 | 2 | 2 |
| Hagglund [44] | 2 | 2 | 2 | 3 | 2 |
| Hale [34] | 2 | 3 | 3 | 2 | 2 |
| Pai [45] | 2 | 1 | 1 | 1 | 1 |
| Nundy [35] | 3 | 2 | 2 | 2 | 2 |
| Piette [46] | 2 | 2 | 2 | 2 | 2 |
| Portz [36] | 2 | 3 | 1 | 2 | 2 |
| Scherr [47] | 2 | 3 | 2 | 2 | 2 |
| Seto [48] | 2 | 2 | 2 | 2 | 2 |
| Suh [37] | 3 | 3 | 2 | 2 | 2 |
| Triantafylidis [38] | 3 | 1 | 2 | 2 | 1 |
| Zan [39] | 3 | 3 | 3 | 2 | 2 |
| Zhang [40] | 3 | 2 | 3 | 3 | 2 |
aHigh risk of bias.
bLow risk of bias.
cUnknown risk of bias.