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Evaluation of risk of bias in the three included studies
| study | sequence generation | allocation sequence concealment | blinding of participants and personnel | blinding of outcome assessment | incomplete outcome data | selective outcome reporting | other potential threats to validity |
|---|---|---|---|---|---|---|---|
| Gao 2007[20] | high | high | high | high | low | N/A | low |
| Yang 2010[21] | N/A | high | high | high | low | N/A | low |
| Liu 2010[22] | N/A | high | high | high | low | N/A | low |
N/A=no information available
