Table 2.
Risk of bias in included studiesa.
| Study (reference) | Selection bias | Performance bias | Detection bias | Attrition bias | Proportion bias | Outcome bias | Reportin bias | Treatmen efficacy | |
| Random sequence generation | Allocation concealment | Blinding of participants and personnel | Blinding of outcome assessment | Incomplete outcome data | Groups balanced at baseline | Groups received same intervention | Selective reporting | Intention-to-treat analysis | |
| Akhu-Z et al, 2016 [17] | Low | Unclear | Unclear | Low | High | Low | Low | Low | High |
| Chow et al, 2015 [18] | Low | Low | Low | Low | High | Low | High | Low | High |
| Dale et al, 2015 [19] | Low | Low | Low | High | Low | High | High | Low | Low |
| Devi et al, 2014 [20] | Low | Low | Low | High | High | Low | Low | High | Unclear |
| Frederix et al, 2015 [21] | Low | Low | Low | Low | High | Low | Low | Low | Unclear |
| Hawkes et al, 2012 [22] | Low | High | Low | Low | High | Low | Low | High | Unclear |
| Johnston et al, 2016 [23] | Low | Unclear | Unclear | Unclear | High | High | High | High | Unclear |
| Kamal et al, 2015 [24] | Low | Low | Low | Low | High | Low | High | Low | High |
| Khonsari et al, 2015 [25] | Low | Unclear | High | Unclear | Low | Low | High | Low | Low |
| Kraal et al, 2014 [26] | Low | Low | Unclear | Unclear | Low | Low | High | Low | Low |
| Lear et al, 2014 [27] | Low | Low | Low | Low | High | Low | Low | Low | Low |
| Maddison et al, 2014 [28] | Low | Low | Low | Low | High | Low | High | Low | Unclear |
| Ogren et al, 2018 [29] | Low | Low | High | Unclear | Low | Low | Low | Unclear | High |
| Pandey et al, 2014 [30] | Unclear | Unclear | Low | Low | Unclear | Low | Low | Unclear | Unclear |
| Park et al, 2013 [31] | Low | Low | High | Low | Low | Unclear | Low | Low | Low |
| Quilici et al, 2012 [32] | Low | Low | Unclear | Unclear | High | Low | Low | Low | Unclear |
| Redfern et al, 2009 [33] | Low | Low | Low | Low | Low | Low | Low | Low | Low |
| Reid et al, 2011 [34] | Low | Low | Low | Low | High | Low | Low | Low | Low |
| Southard et al, 2003 [35] | Low | Low | Low | Low | Low | Low | Low | Low | Low |
| Tiede et al, 2017 [36] | Low | Low | High | Unclear | High | High | Low | Low | High |
| Vale et al, 2002 [37] | Low | High | High | Low | High | Low | Low | High | Low |
| Vemooij et al, 2012 [38] | Low | Low | Unclear | Unclear | Low | Low | High | Low | Low |
| Wan et al, 2016 [39] | Low | Low | Low | Low | High | Low | Low | Low | Low |
| Widmer et al, 2017 [40] | Low | Low | Low | Low | Low | High | High | Low | Unclear |
| Zheng et al, 2019 [41] | Low | High | Low | Low | Low | Low | High | Low | Low |
aRisk of bias: review authors’ judgments about each risk of bias item for the included studies.