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William Osler Health System - Resources for Evidence Based Practice: Learn About EBP

Evidence-Based Practice Resources

Research ↪ Evidence ↪ Practice

Welcome! Learn about Evidence Based Practice

Evidence-Based Practice is knowing that what we do is the best practice.

In this guide you will find Evidence-Based Practice tools, as well as recommended databases, books, practice sites, and information about Evidence-Based Research. Evidence-Based Medicine (EBM) is the integration of clinical expertise, patient values and the best research evidence into the decision making process for patient care.

Clinical expertise refers to the clinician’s cumulated experience, education and clinical skills. The patient brings to the encounter his or her own personal preferences and unique concerns, expectations, and values. The best research evidence is usually found in clinically relevant research that has been conducted using sound methodology. (Sackett D, 2002)

Levels of evidence

The levels of evidence pyramid provides a way to visualize both the quality of evidence and the amount of evidence available.       

For example, systematic reviews are at the top of the pyramid, meaning they are both the highest level of evidence and the least common. 

As you go down the pyramid, the amount of evidence will increase as the quality of the evidence decreases.

Understanding the Evidence Pyramid

Studies are assigned levels of evidence based on their methodology. The evidence pyramid is an easy way to visualize this hierarchy of evidence.

At the top of the pyramid is filtered evidence including systematic reviews, meta-analyses, and critical appraisals.  These studies evaluate and synthesize the literature.  The top of the pyramid represents the strongest evidence.

At the base of the pyramid is unfiltered evidence including randomized controlled trials, cohort studies and case reports. These are individual reports and studies, also known as the primary literature. 

You should seek the highest level of evidence available, but remember that evidence at the top of the pyramid might not exist for your particular clinical question. If that is the case, you'll need to move down the pyramid to find the strongest evidence that addresses your clinical question.

Rating System for the Hierarchy of Evidence



Evaluation Criteria


Level I


Evidence from a Systematic Review or Meta-Analysis of all relevant Randomized Controlled Trials (RCTs) or evidence based Clinical Practice Guidelines based on systematic reviews of RCTs

Level II

Evidence obtained from at least one well-designed RCT

Level III

Evidence obtained from well-designed Controlled Trials without Randomization

Level IV

Evidence from well-designed Case-Control and Cohort Studies

Level V

Evidence from Systematic Reviews of descriptive and qualitative studies

Level VI

Evidence from a single descriptive or qualitative study

Level VII

Evidence from the opinion of authorities and /or reports of expert committees

From: Melnyk, Bernadette Mazurek, and Ellen Fineout-Overholt. Evidence-Based Practice in Nursing & Healthcare: A Guide to Best Practice

      Image source: Georgetown University Medical Centre                   

EBP Books Available Online!

Research → Evidence → Practice

Research Generate Evidence to Improve Practice


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