Table 2.
Risk of Bias Assessment.
| Study Authors (year) | Random Sequence Generation (Selection bias) | Allocation Concealment (Selection bias) | Blinding of Participants and Personnel (Performance bias) | Blinding of Outcome Assessment (detection bias) | Incomplete Outcome data (Attrition bias) | Selective Reporting (Reporting bias) | Other bias |
|---|---|---|---|---|---|---|---|
| Ryvlin et al (2014)31 | Low | High | High | High | High | High | Unclear |
| Klinkenberg et al (2012) 28 | Low | Low | Unclear | Unclear | Low | High | Unclear |
| DeGiorgio et al (2005)29 | Low | Unclear | High | High | Low | Low | Low |
| Handforth et al (1998)26 | Low | Low | Unclear | Unclear | Low | Low | Unclear |
| Scherrmann et al, (2001)30 | Unclear | High | High | High | Low | High | Low |
| VNS group et al (1995)25 | Low | Low | Unclear | Unclear | Unclear | Low | Unclear |
| Michael et al (1993)27 | Unclear | Unclear | Unclear | Unclear | Low | Low | Unclear |