Table 2.
Risk of bias assessment included in the meta-analysis.
| No. | Reference | Selection of participants | Confounding variables | Measurement of exposure | Blinding of outcome assessment | Incomplete outcome date | Selective outcome reporting |
|---|---|---|---|---|---|---|---|
| 1 | Han et al. [29] | L | H | L | L | L | L |
| 2 | Yang et al. [24] | L | L | L | L | L | L |
| 3 | Bouchi et al. [30] | L | H | L | L | L | L |
| 4 | Hwang et al. [23] | L | L | L | L | L | L |
| 5 | Yoon et al. [31] | L | L | L | L | L | L |
| 6 | Chung et al. [22] | L | H | L | L | L | L |
Abbreviations: L: low risk of bias; U: unclear risk of bias; H: high risk of bias.