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Physician Assistant Program: Evidence Based Practice

Selected Resources for physician assistant students.

Evidence Based Practice Process

Why Evidence Based Practice?

There is a substantial gap between the best research evidence and clinical practice with potentially serious health consequences for patients. Key reasons for the research-practice gap include lack of time and skills needed for finding and appraising the evidence. Evidence based practice helps bridge that gap by providing strategies that facilitate finding and appraising research, and resources that pre-filter and synthesize research to make the process more efficient.                                              Strauss, S. E. (2011)


The 5 "A's" will help you to remember the EBP process:

  1. ASK:  Information needs from practice are converted into focused, structured questions (PICO).
  2. ACQUIRE:  The focused questions are used as a basis for literature searching in order to identify relevant external evidence from research. (Develop a search strategy to find resources to answer the question(s).
  3. APPRAISE:  The research evidence is critically appraised for validity. (Are the individual results valid, reliable, applicable?)
  4. APPLY: The best available evidence is used alongside clinical expertise and the patient's perspective to plan care. (Determine the clinical significance of research to the target population, including benefits and risks.)
  5. ASSESS:  Performance is evaluated through a process of self reflection, audit, or peer assessment.

PICOT Question

Asking the Question:

The first step in research or evidence-based practice is defining a problem and asking a question.  It is recommended that you formulate your question using the PICO (or PICOT) concept to search for quantitative studies. The PICO format provides a consistent, systematic way to identify the components of a clinical issue.

Critical Appraisal tools

Critical appraisal is the systematic evaluation of clinical research papers in order to establish:

  1. Does this study address a clearly focused question?
  2. Did the study use valid methods to address this question?
  3. Are the valid results of this study important?
  4. Are these valid, important results applicable to my patient or population?

If the answer to any of these questions is “no”, you can save yourself the trouble of reading the rest of it.


This section contains useful tools and downloads for the critical appraisal of different types of medical evidence. Example appraisal sheets are provided together with several helpful examples.

Critical Appraisal Worksheets (from Darmouth University)

Evidence Based Pyramid


One way to organize the different types of evidence involved in evidence-based practice research is the levels of evidence pyramid.

On this page you will find an image of the evidence pyramid as well as links to databases, websites, and journals where you can find:

  • Filtered resources

    • systematic reviews

    • critically-appraised topics

    • critically-appraised individual articles

  • Unfiltered resources

    • randomized controlled trials

    • cohort studies

    • case-controlled studies, case series, and case reports

  • Background information, expert opinion


Levels of evidence pyramid

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.

EBM Pyramid and EBM Page Generator, copyright 2006 Trustees of Dartmouth College and Yale University. All Rights Reserved.
Produced by Jan Glover, David Izzo, Karen Odato and Lei Wang.

Filtered Resources

Filtered resources appraise the quality of studies and often make recommendations for practice. The main types of filtered resources in evidence-based practice are:

  • systematic reviews
  • critically-appraised topics
  • cirtically-appraised individual articles

Below you will find links to resources where you can find each of these types of filtered information.


Systematic reviews

Authors of a systematic review ask a specific clinical question, perform a comprehensive literature review, eliminate the poorly done studies, and attempt to make practice recommendations based on the well-done studies. Systematic reviews include only experimental, or quantitative, studies, and often include only randomized controlled trials.

You can find systematic reviews in these filtered databases:


Critically Appraised Topics

Authors of critically-appraised topics evaluate and synthesize multiple research studies.

Critically Appraised Individual Articles

Authors of critically-appraised individual articles evaluate and synopsize individual research studies.


Unfiltered Information

Evidence is not always available via filtered resources.  Unfiltered or primary sources provide evidence concering a topic under investigation.  Primary resources are generally articles that appear in peer-reviewed journals and are are found by primarily searching databases.

What kinds of studies are relevant?

  • Clinical Trials
  • Randomized Control Trials
  • Multicentre Studies
  • Epidemiology Studies
  • Prospective Studies
  • Retrospective Studies
  • Cohort Studies
  • Case Control Studies


Randomized Controlled Trials

Randomized controlled trials in humans are used to test the safety and potential benefit of a treatment. While the harms of a treatment sometimes prove to outweigh the benefits, this form of testing is acceptable to the participants because the investigators are aiming at the outset to develop a new treatment and usually have a reasonable expectation of safety at least, if not a positive effect of treatment.


Cohort Studies

Cohort studies are a type of medical research used to investigate the causes of disease, establishing links between risk factors and health outcomes.  Cohort studies are observational - the researchers simply observe what happens, without applying any intervention themselves.

Case-Controlled Studies, Case Series, Case Reports

A case-control study is a type of medical research investigation often used to help determine the cause of a disease, particularly when investigating a disease outbreak or a rare condition. This is usually retrospective -- the researchers look back at data collected in the past, enabling them to test whether a particular outcome can be linked back to a suspected risk factor.


Background Information