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Evidence Based Medicine

Information and resources about using EBM in patient care.

Find the best study design for your question

Clinical Question Suggested Best Study
Harm/Etiology RCT > cohort > case control > case series
Clinical Exam prospective, blind comparison to gold standard
Diagnosis prospective, blind comparison to gold standard
Therapy RCT > cohort > case control > case series
Prevention RCT > cohort study > case control > case series
Prognosis cohort study > case control > case series
Cost Benefit economic analysis

adapted from Duke Libraries' Introduction to Evidence Based Practice


One way to organize the different types of evidence involved in evidence-based practice research is the levels of evidence pyramid. The pyramid includes a variety of evidence types and levels.

  • 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

Pyramid of Evidence

Image based on 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.

Definitions of Study Types

(From CEBM's Glossary and Duke Libraries' Intro to Evidence-Based Practice)

Case report / Case series: A report on a series of patients with an outcome of interest. No control group is involved.

Case control study: A study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest.

Cohort study: Involves identification of two groups (cohorts) of patients, one which received the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.

Randomized controlled clinical trial: Participants are randomly allocated into an experimental group or a control group and followed over time for the variables/outcomes of interest.

Systematic review: A summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate statistical techniques to combine these valid studies.

Meta-analysis: A systematic review that uses quantitative methods to synthesize and summarize the results.

Cross sectional study: The observation of a defined population at a single point in time or time interval. Exposure and outcome are determined simultaneously.

Prospective, blind comparison to a gold standard: Studies that show the efficacy of a diagnostic test are also called prospective, blind comparison to a gold standard study. This is a controlled trial that looks at patients with varying degrees of an illness and administers both diagnostic tests — the test under investigation and the “gold standard” test — to all of the patients in the study group. The sensitivity and specificity of the new test are compared to that of the gold standard to determine potential usefulness.

Qualitative research: answers a wide variety of questions related to human responses to actual or potential health problems.The purpose of qualitative research is to describe, explore and explain the health-related phenomena being studied.

Retrospective cohort: follows the same direction of inquiry as a cohort study.  Subjects begin with the presence or absence of an exposure or risk factor and are followed until the outcome of interest is observed.  However, this study design uses information that has been collected in the past and kept in files or databases.  Patients are identified for exposure or non-exposures and the data is followed forward to an effect or outcome of interest.

Filtered Information

 Systematic Reviews

▲ Critically-Appraised Topics

Evaluate and synthesize multiple research studies.

 Critically-Appraised Articles

Evaluate and synthesize individual research studies.

Unfiltered Information

▲ ▲  Unfiltered Information

Literature databases for RCTs, cohort studies, case-controlled studies, case series, etc.)

Background Information & Expert Opinion

 Background Information/ Textbooks

Evidence in these resources may vary from expert opinion to high levels of evidence.

Other Resources

Evidence in these resources may vary from expert opinion to high levels of evidence.

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