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Physical Therapy Research Guide

Levels of Evidence

There are many evidence hierarchies available. Variations of the evidence pyramid below are some of the most widely used. These tools can help conceptualize the reasearch landscape, but beware of applying them too rigidly. Different study types are best suited to answer different types of clinical questions, and a well-designed study of a type lower on the pyramid may be more credible than a poorly-designed study of a type higher on the pyramid.

Explore the resources on this page for more information about levels of evidence and evaluating studies for validity and bias.


*Book and resource reviews

Credit: Bradley A. Long [author] and Eliza Donne [graphic designer]. 2nd ed. Harrell Health Sciences Library. Penn State College of Medicine. (2020). Creative Commons License:

Rating Scales

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Critical Appraisal Resources

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