Figure 3. Risk of bias assessment using the Cochrane tool.

D1: Bias due to confounding, D2: bias arising from measuring of the exposure, D3: bias in the selection of participants into the study (or into the analysis), D4: bias due to post-exposure interventions, D5: bias due to missing data, D6: bias arising from the measurement of the outcome, D7: bias in the selection of the reported result

Red circles: high risk of bias, yellow circles: some concerns, green circles: low risk of bias