Table 2 Assessment of bias using the Office of Health Assessment and Translation (OHAT) tool
Author (Year) | Selection bias | Confounding bias | Attrition/ exclusion bias | Exposure characterization | Outcome assessment | Selective reporting bias | Appropriate Statistical Methods | Overall Study Confidence |
|---|---|---|---|---|---|---|---|---|
Bazyka (2012) [26] |  + +  | – |  + +  | – |  + +  |  + +  | - | Tier 3 |
Boice (2009) [44] |  +  | - |  + +  | – |  +  |  + +  | - | Tier 3 |
Bunch (2014) [65] | - | – | - | – | - |  + +  | - | Tier 3 |
Demoury (2020) [54] |  + +  | - |  + +  | - |  + +  |  + +  |  +  | Tier 2 |
Desbiolles (2017) [33] | - | - |  + +  | – |  + +  |  + +  |  + +  | Tier 3 |
Gulis (1998) [64] |  + +  | – |  + +  | - |  + +  |  + +  | - | Tier 3 |
Kim (2018) [47] |  + +  |  + +  |  + +  | - |  + +  |  + +  |  + +  | Tier 2 |
Lane (2013) [39] |  + +  | - |  + +  |  +  |  + +  |  + +  | - | Tier 2 |
Salerno (2016) [63] |  +  | – |  + +  | – |  +  |  + +  | - | Tier 3 |
Wang (2016) [66] |  + +  | – |  + +  | - |  + +  |  + +  | - | Tier 3 |
Zadnik (2008) [46] |  + +  | – |  + +  | – |  + +  |  + +  | - | Tier 3 |