Levels of Evidence Pyramid

Clinicians must also understand the types of evidence and their relative quality in the hierarchy of research evidence.  The Evidence Pyramid below represents the relative quality of types of evidence with the least clinically relevant at the bottom and the most clinically relevant at the top.  Remember, as you move up the pyramid, the amount of available literature decreases, increases in relevance to the clinical setting.

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Please review the following link for a description of the "Types of Design Types" (American University of Beirut Saab Memorial Medical University Library, n.d.).   

Levels of Evidence Hierarchy

The Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence​ provides a ranking system reflecting the quality/rigor of the research and strength of the results, and associated confidence in applying the results into clinical decision-making with clients. 

Case series and Case reports: consist of collections of reports on the treatment of individual patients or a report on a single patient. Because they are reports of cases and use no control groups to compare outcomes, they have little statistical validity.

Case control studies:  studies in which patients who already have a specific condition are compared with people who do not have the condition. The researcher looks back to identify factors or exposures that might be associated with the illness.  They often rely on medical records and patient recall for data collection. These types of studies are often less reliable than randomized controlled trials and cohort studies because showing a statistical relationship does not mean than one factor necessarily caused the other. 

Cohort studies: identify a group of patients who are already taking a particular treatment or have an exposure, follow them forward over time, and then compare their outcomes with a similar group that has not been affected by the treatment or exposure being studied. Cohort studies are observational and not as reliable as randomized controlled studies, since the two groups may differ in ways other than in the variable under study.  

Randomized controlled clinical trials:  carefully planned experiments that introduce a treatment or exposure to study its effect on real patients. They include methodologies that reduce the potential for bias (randomization and blinding) and that allow for comparison between intervention groups and control (no intervention) groups.  A randomized controlled trial is a planned experiment and can provide sound evidence of cause and effect.  

Systematic Reviews:  focus on a clinical topic and answer a specific question. An extensive literature search is conducted to identify studies with sound methodology. The studies are reviewed, assessed for quality, and the results summarized according to the predetermined criteria of the review question.

A Meta-analysis: will thoroughly examine a number of valid studies on a topic and mathematically combine the results using accepted statistical methodology to report the results as if it were one large study.  

• Duke University (2016b):  Introduction to Evidence-Based Practice 

With so much available on the internet, it is easy to find information on just about every topic.  But is it appropriate information for graduate or professional work?  To help understand the expectations for appropriate scholarly literature, review the following video and resources: 

• How to Recognize Peer-Reviewed (Refereed) Journals
• What is Peer-Review? 

To be able to locate scholarly literature, often you can use professional databases.  We have access to  CINAHL Complete (through NC AHEC), PsycARticles (through NC AHEC), and PubMed to name a few.  If you have questions on how to use these databases, please feel free to contact either Cassie Dixon for assistance. 

Below are links to sites that provide definitions of medical terms.