- Red circle, high risk of bias; yellow circle, moderate risk of bias; green circle, low risk of bias. D1: bias due to confounding data (selection bias), D2: bias in selection of participants into the study (selection bias), D3: bias in classification of interventions (information bias), D4: bias due to deviations from intended interventions (performance bias), D5: bias due to missing data (attrition data), D6: bias in measurement of outcomes (detection bias), and D7: bias in selection of the reported result (outcome reporting bias)