Table 2.
Evaluation of risk of bias in the included studies based on the seven items in the Cochrane Risk of Bias (ROB) tool[29]
| Study ID | random sequence generation |
allocation concealment |
blinding of participants and providers |
blinding of outcome assessment |
incomplete outcome data |
selective reporting |
other biasesa |
OVERALL RISK OF BIASb |
|---|---|---|---|---|---|---|---|---|
| Xu 2006[24] | low | unclear | low | low | low | low | low | Unclear |
| Shim 2007[18] | unclear | unclear | unclear | unclear | low | low | low | Unclear |
| Zhang 2008[38] | low | unclear | low | low | low | low | low | Unclear |
| Ji 2008[39] | low | unclear | low | low | low | low | low | Unclear |
| Jin 2008[40] | low | unclear | unclear | unclear | low | low | low | Unclear |
| Chen 2009[20] | low | unclear | low | unclear | low | low | low | Unclear |
| Kane 2009[19] | unclear | unclear | unclear | unclear | low | low | low | Unclear |
| Wang 2009[41] | unclear | unclear | low | unclear | low | low | low | Unclear |
| Song 2009[42] | low | unclear | low | low | low | low | low | Unclear |
| Chen 2010[21] | unclear | unclear | low | unclear | low | low | low | Unclear |
| Liu (L) 2011[43] | unclear | unclear | unclear | unclear | unclear | high | low | High |
| Liu (Z) 2011[44] | unclear | unclear | high | unclear | low | low | low | High |
| Sun 2011[45] | unclear | unclear | high | unclear | low | high | low | High |
| Xue 2012[46] | unclear | unclear | low | low | low | low | low | Unclear |
| Zhou 2012[47] | unclear | unclear | low | unclear | low | low | low | Unclear |
| Zhu 2012[48] | unclear | unclear | low | unclear | low | low | low | Unclear |
| Wu 2013[49] | unclear | unclear | high | unclear | unclear | low | low | High |
| Guo 2013[50] | unclear | unclear | high | unclear | low | low | low | High |
| Chen 2014[27] | unclear | unclear | low | low | low | low | low | Unclear |
| Pan 2014[51] | low | unclear | unclear | unclear | unclear | low | low | Unclear |
| Qiao 2015[52] | unclear | unclear | high | unclear | low | low | low | High |
| kappac | 1.00 | 0.62 | 0.30 | 0.79 | 1.00 | 1.00 | 1.00 | 0.62 |
a Other biases considered include study-specific biases or concerns about fraudulent results
b If any of seven items are coded high-risk of bias the overall study is classified as high-risk, if all seven items are coded as low-risk the overall study is classified as low-risk; all other studies (i.e., those with some items coded a ‘unclear’ and no items coded as high-risk) are classified as ‘unclear’
c Kappa values for inter-rater reliability of the two independent coders who assessed for each item for the 21 studies