As part of the Institute of Education Sciences' (IES) goal to help educators and policymakers incorporate scientifically based research into their work, the What Works Clearinghouse (WWC) has established rigorous standards for the review of causal research. Studies are first subjected to a set of screening standards to determine relevance to the topic at hand. Those studies deemed relevant are then rated according to WWC Evidence Standards and assigned one of three ratings.
These technical standards and their application are regularly updated to take account of new considerations brought forth by experts and users. Such changes may result in re-appraisals of studies and/or interventions previously reviewed and rated. Current WWC standards offer guidance for those planning or carrying out studies, not only in the design considerations but the analysis and reporting stages as well. For more information about technical studies and their implementation, please see the WWC Document Library. For answers to frequently asked questions concerning WWC's research, review, and standards, please see the WWC Research, Review, and Standards FAQ.
Ratings
- Meets Evidence Standards: Studies assigned this rating are generally well-conducted randomized controlled trials (RCTs) that do not have problems with randomization or attrition, or regression discontinuity designs that do not have problems with attrition.
- Meets Evidence Standards with Reservations: Generally, studies assigned this rating are strong quasi-experimental studies that have comparison groups with demonstrated equivalence and meet other WWC Evidence Standards. Studies assigned this rating may also include randomized trials with problems in randomization or attrition, as well as regression discontinuity designs with attrition problems.
- Does Not Meet Evidence Standards: These are studies that provide insufficient evidence of causal validity.
