Quality Assessment of Studies and Risk of Bias for Each Study Considered
| Study | Design | Selection bias | Reporting bias | Reference standard |
| Randolph (2002) | High | High | High | High |
| Hoyes (2004) | High | High | Low | High |
| Bal (2006) | Unclear | High | High | High |
| Santra (2011) | High | High | High | High |
| Giovanella (2013) | Low | Low | Low | Low |