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Evidence-Based Practice

Levels of Evidence

Levels of Evidence Pyramid

Publication types are ranked in evidence pyramids based on the rigor of evidence provided by the research design.  The higher the study design is on the pyramid, the higher the level of evidence.  However, this also means there are fewer documents of this type.

High level evidence from the top of the pyramid is preferred, but not always available for all questions.  Remember that the type of question you are asking will help determine which types of studies would be most appropriate.

Check out the links below for more information of the different levels of evidence and research study designs.


Question Type & Study Design

What type of question you are trying to answer (e.g. therapy, diagnosis, etc.) will directly affect what types of evidence you can expect or hope to find.  For example, a therapy question would ideally be answered by a randomized controlled trial.  However, it is not very ethical to randomize people to experience a potential harm, so an etiology question may be more appropriately answered by a cohort or case-control study.

When assessing the evidence you are finding, you want to aim for the top of the pyramid, but also consider if that evidence would exist and what type of study would best encompass it.

Question Type Best Evidence
  • Randomized Controlled Trials
  • Diagnostic Validation Studies (compare new & gold standard tests)
  • Cohort Studies
  • Case-Control Studies
  • Cohort Studies
  • Case-Control Studies

Is this Scholarly?

The research evidence integrated in Evidence-Based Practice should come from scholarly sources.  If you are unsure whether you are using a scholarly article, the following resources can help.

Video created by University of Washington Libraries.  This video is licensed under a Creative Commons Attribution 4.0 International License.