Table 3 Risk of bias assessment
Study | Selection bias | Performance bias | Attrition bias | Reporting bias | Other sources of bias | Overall risk of bias | |
|---|---|---|---|---|---|---|---|
Random sequence generation | Allocation concealment | Blinding of participants and personnel | Incomplete outcome data | Selective reporting | |||
Gans 1990 [37] | Low risk | Low risk | Unclear risk | Unclear risk | Unclear risk | Low risk | Unclear risk |
Leng 1998 [34] | Low risk | Low risk | Low risk | High risk¶ | Unclear risk | Unclear risk* | High risk |
Carrero 2005 [35] | Low risk | Unclear risk | Low risk | Unclear risk | Unclear risk | High risk§ | High risk |
Carrero 2006 [36] | Low risk | Unclear risk | Low risk | Unclear risk | Unclear risk | High risk§ | High risk |
Ishikawa 2010 [38] | Low risk | Unclear risk | Unclear risk | Unclear risk | Unclear risk | Low risk | Unclear risk |