Table 2. Risk of bias assessment.
| Study | Bias arising from the randomization process | Bias due to deviations from intended interventions | Bias due to missing outcome data | Bias in measurement of the outcome. | Bias in selection of the reported result | Overall risk of bias judgement |
|---|---|---|---|---|---|---|
| (1st author, year) | ||||||
| Moon YE, 2012 | Low risk | Low risk | Low risk | Low risk | Low risk | Low risk |
| Ewalenk P, 1996 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Metaxari M, 2011 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Zhou H, 2012 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Park JW, 2012 | Some concerns | Low risk | Low risk | Some concerns | Low risk | High risk |
| Jeon Y, 2010 | Low risk | Low risk | Low risk | Low risk | Low risk | Low risk |
| Doksrod S, 2012 | Low risk | Low risk | Low risk | Some concerns | Low risk | Some concerns |
| Barros A, 2013 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Schietrom M, 2013 | Low risk | Low risk | Low risk | Low risk | Low risk | Low risk |
| Eberhar LH, 1999 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Song YK, 2013 | Low risk | Low risk | Low risk | Some concerns | Low risk | Some concerns |
| Akin A, 2006 | Some concerns | Low risk | Low risk | Some concerns | Low risk | High risk |
| Tarantino I, 2015 | Low risk | Low risk | Low risk | Low risk | Low risk | Low risk |
| Fujii Y, 2007 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Papadima A, 2013 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Lee DC, 2011 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Tavlan A, 2006 | Low risk | Low risk | Low risk | Low risk | Low risk | Low risk |
| Lee SY, 2002 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Wang JJ, 1999 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Zhang HW, 2016 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Kim WJ, 2013 | Low risk | Low risk | Low risk | Low risk | Low risk | Low risk |
| Worni M, 2008 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Wang JJ, 2000 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Fujii Y, 2001 | Some concerns | Low risk | Low risk | Low risk | Low risk | Some concerns |
| Jokela R, 2002 | Low risk | Low risk | Low risk | Some concerns | Low risk | Some concerns |
| Lee MJ, 2015 | Low risk | Low risk | Low risk | Low risk | Low risk | Low risk |