Risk of bias assessment: non-randomised studies (Cochrane Risk Of Bias In Non-randomized Studies – of Interventions Tool)
| Study | Confounding | Participant selection | Classification of interventions | Deviation from intended intervention | Missing data | Outcome measurement | Selective outcome reporting | Overall |
| Everhart et al 64 | Low | Low | Low | Low | Low | Moderate | Low | Moderate |
| Heijne et al 66 | Low | Low | Low | Low | Low | Low | Low | Low |