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

Evidence-Based Practice Resources


Research Generate Evidence to Improve 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.

Filtered Information (secondary literature)

Systematic Review - Uses explicit rigorous methods to identify, critically apprise, and synthesize relevant studies

Meta Analysis - A quantitative method of combining the results of independent studies and synthesizing summaries and conclusions that may be used to evaluate therapeutic evidence

Critically Apprised Topic (CAT's) - A summary of the best evidence on a topic. CAT's usually include evidence from more than one study, are brief and their methods are less rigorous than SR

Critically Appraised Individual Article - A summary of a single paper, authors evaluate and synopsize individual research study

Unfiltered Information (primary literature)

Randomized Controlled Trial - A clinical trial that subjects are assigned randomly to one of two groups with one group is receiving intervention and is tested and the other is receiving alternative treatment and the follow up

Cohort Study - An observational study that compares two groups with exposure of interest and control one (no exposure)

Case Control Trial - A study that identifying subjects with disease of interest and control group without the disease and comparison

Clinical Trial -  Pre-planned studies to answer questions on safety or efficacy of specific interventions according to protocol or research plan created by investigators

   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                   



Recommended EBP Books - Available!

EBP Books Available Online!