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Health Sciences

A guide to tools and resources for students in the CWU Health Science degree and certificate programs

Hierarchy of Evidence

Research design and evidence

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The Hierarchy of Evidence is a way to rank information in order to find the best evidence available. This is a part of Evidence-Based Practice (EBP); the search for strong evidence. Information near the top has undergone a thorough review process while those near the bottom have not and may be weak sources. Experts differ on their arrangement of the hierarchy within the filtered and unfiltered sections depending on the type of question they are trying to answer but this is a general order.


Filtered Information

Filtered information is also called secondary or pre-appraised information. This is primary literature (original, unfiltered data or reports) that has been reviewed, sometimes over a long period of time, for accuracy and looks at how to apply it to practice. 

Unfiltered Information

This is the raw, original data or reports. It has not been reviewed by as extensively as filtered information and may still have some flaws or bias. They are also much more difficult to interpret and apply to practice because of the lack of review.

Where to go for different levels of the hierarchy

Filtered Information: Meta-Search Engines

These databases locate resources at multiple levels in the hierarchy.

Filtered Information

These databases and journals contain systematic reviews/meta-analyses, critically-appraised topics, and critically-appraised articles.

Some of these you may have to login using your CWU credentials or search for the journal title in the database Web of Science.

Unfiltered Information

These databases and journal contain Randomized Controlled Trials (RCTs), case cohorts, and control studies.