The quality of the study is high, meaning we can be fairly confident in the study findings. Strong evidence shows that the study finding is solely attributable to the intervention examined. This rating is reserved for study findings from high quality RCTs with low attrition of sample members.

The quality of the study is moderate, meaning we can be somewhat confident in the study findings. However, other factors not accounted for in the study might also have contributed to the findings. This applies to findings from random assignment studies that, because of flaws in the study design or analysis (for example, high sample attrition), do not meet the criteria for the high rating but satisfy other design criteria. We also assign the moderate rating to study findings from well-executed QEDs.

The quality of the study is low, meaning we cannot have much confidence in the study findings. Other important factors could have influenced the study findings, and the study did not account for them. Study findings that do not meet the high or moderate ratings criteria receive the low rating.