Table 5.
Risk of Bias Assessment: Newcastle-Ottawa Quality Assessment Scale.
| NO | Reference | Case definition |
Representativeness of cases |
Selection of controls | Definition of controls | Comparability by design and analysis | Ascertainment of exposure | Same method of ascertainment for cases and controls | Nonresponse rate | Score |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Zadik (2008) | * | * | X | X | * | * | * | * | 7 |
| 2 | Keller (2012) | * | * | * | * | ** | * | * | * | 9 |
| 3 | Oguz (2012) | * | * | * | * | ** | * | * | * | 7 |
| 4 | Tsao (2014) | * | * | * | * | ** | * | * | * | 9 |
| 5 | Martin (2018) | * | * | * | * | ** | * | * | * | 9 |
| 6 | Chou (2018) | * | * | * | * | *X | * | * | * | 8 |
Note. *indicates that the feature is present; x, that the feature is absent. But for comparability by design this checklist awards maximum of two stars (**), one (*) or none if the feature is completely absent.