Table 2.
Risk of bias of included studies
| Author | Year | Bias domain | ||||||
|---|---|---|---|---|---|---|---|---|
| Bias due to confounding | Bias in selection of participants into the study | Bias in classification of exposure | Bias due to missing data | Bias in measurement of outcomes | Bias in selection of the reported result | Overall | ||
| Alwasel | 2011 | Low/Moderate | Low | Serious | Low | Low | Low | Moderate |
| Arab | 2001 | Low | Low | Low | Serious | Low | Low | Moderate |
| Awwad | 2012 | Moderate | Low | Low | Low | Low | Low | Low |
| Azizi | 2014 | Low | Low | Low | Moderate | Low | Low | Low |
| Bayoglu Tekin | 2016 | Low | Low | Low | Low | Low | Low | Low |
| Daley | 2018 | Moderate | Low | Moderate | Moderate | Low | Low | Moderate |
| Hefni | 1993 | Low/Moderate | Low | Low | Low | Low | Low/Moderate | Low |
| Hizli | 2012 | Low | Low | Low | Low | Low | Low | Low |
| Karateke | 2016 | Moderate | Low | Low | Low | Low | Low | Low |
| Kavehmanesh | 2004 | Low/Moderate | Low | Low | Low | Low/Moderate | Low | Low |
| Malhotra | 1989 | Moderate | Low | Low | Low/Moderate | Low | Low | Moderate |
| Makvandi | 2013 | Moderate | Low | Low | Low | Low | Low | Low |
| Naderi | 2004 | Moderate | Low | Low | Low | Low | Low | Low |
| Ozturk | 2011 | Moderate | Low | Low | Low | Low/Moderate | Low | Low |
| Petherick | 2014 | Moderate/Serious | Low | Moderate | Low | Low | Low | Moderate |
| Rezk | 2016 | Low | Low | Low | Low | Low | Low | Low |
| Sakar | 2016 | Low | Low | Low | Low | Low | Low | Low |
| Sarafraz | 2013 | Low | Low | Low | Low | Low | Low | Low |
| Savitri | 2018 | Low | Serious | Low | Low | Low | Low | Moderate |
| Seckin | 2014 | Low | Low | Low | Low | Low | Low | Low |
| Shahgheibi | 2005 | Low/Moderate | Low | Low | Low | Low | Low | Low |
| Ziaee | 2010 | Low | Low | Low | Low | Low | Low | Low |
Studies found to have a moderate or greater risk of bias in one or more domains are highlighted in bold