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Pyramid of Evidence

Acquire the Evidence from appropriate sources.

Many resources are currently available. You must learn to appreciate the pros and cons of each type to determine when each can best be applied.

You also have to learn how to access resources that can maximize your efficiency, such as a systematic review, guideline, or article synopsis.

What types of studies or data will be most helpful in answering your question?

Medical literature is immense, but only a small portion is immediately useful in answering clinical questions. The literature reports the whole spectrum of the scientific research process from in-vitro studies to double-blind randomized control trials. This spectrum is called the “wedge of evidence” or the “pyramid of evidence.”

TRIP (Turning Research Into Practice)
Trip is a clinical search engine designed to allow users to quickly and easily find and use high-quality research evidence to support their practice and/or care. As well as research evidence, TRIP allows clinicians to search across other content types including images, videos, patient information leaflets, educational courses and news.

Definitions of Types of Studies


Systematic Reviews

Evidence Syntheses

Article synopses

Randomized Controlled Trials

Crossover Design

Cohort Studies

Case Controlled Studies

Cross-Sectional Study

Difference Between Cohort, Case-Controlled, and Cross-Sectional Studies -- Time is the Key

Case Series/Case Reports

Background Information/Expert Opinion

Study Design Levels Levels of Evidence

Evidence-based medicine involves tracking down the available evidence, assessing its validity and then using the “best” evidence to inform decisions regarding care. Rules of evidence have been established to grade evidence according to its strength. The terms "levels of evidence" or "strength of evidence" refer to systems for classifying the evidence in a body of literature through a hierarchy of scientific rigor and quality. Several dozen of these hierarchies exist. Some systems comprise three levels and others eight or more.

Where will you search?

Filtered Resources

Systematic Reviews / Meta-Analyses


This resource is a regularly updated collection of evidence-based medicine databases. It includes abstracts and full reviews of controlled trials, methodologies, economic evaluation, and health technology assessment. Many consider the Cochrane Database of Systematic Reviews to be the “gold standard” of systematic reviews.

Systematic Reviews and Meta-Analyses are also searchable in MEDLINE:

  • PubMed Select "Clinical Queries" or perform a search and then select "Meta-Analysis" and/or "Systematic Reviews" from the list of "Article Types."

  • Embase Select "Cochrane Review", "Systematic Review" and/or "Meta Analysis"

  • PICO searching from NLM is a specialty interface where Patient/Problem, Intervention, Compare to, and Outcome factors are entered to search MEDLINE. Choose "Meta-Analysis" from the "Select Publication Type" pull-down menu. Not geting any results? Don't select any publication type.

  • Already have your PICO Question formulated, use askMEDLINE, a free-text, natural language search tool for MEDLINE/PubMed.

Critically-Appraised Topics


Combines the clinical expertise and curated disease content of DynaMed with the comprehensive drug information of Micromedex. This integration allows faculty, staff and learners to access evidence-based recommendations and drug dosing, interaction, and IV compatibility information in one tool.

Critically-Appraised Individual Articles

The ACP Journal Club

The editors of this journal screen the top 100+ clinical journals and identify studies that are methodologically sound and clinically relevant. An enhanced abstract, with conclusions clearly stated, and a commentary are provided for each selected article. Published by the American College of Physicians-American Society of Internal Medicine.

Unfiltered Resources


Discovery is an online tool that "pulls together" almost all of the resources of our Libraries so that they can be explored using a single search box. Think of Search Everything as the MUSM Libraries' version of Google.


To limit your PubMed search to the best evidence-producing studies: Click on "clinical queries" (on the left side of the screen). This specialized search is intended for clinicians and has built-in search "filters." Four study categories--therapy, diagnosis, etiology, prognosis--are provided, and you may indicate whether you wish your search to be more sensitive (i.e., include most relevant articles but probably including some less relevant ones) or more specific (i.e., including mostly relevant articles but probably omit a few).

Clinical Key

Provides access to 900+ books, 500+ journals, the First Consult point of care database, over 1 million images, and 3,000+ videos from Procedures Consult..


International coverage of the professional and academic literature in psychology, medicine, psychiatry, nursing, sociology, education, pharmacology, physiology, linguistics, and other areas.

To limit your PsycINFO search to the best evidence-producing studies: Click on the "Limits" icon to use "Clinical Queries" or limit to "methodology" types.

Background Information/Expert Opinion

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


Has over 10,000 physician authors and editors who create thousands of peer-reviewed, disease specific articles. Includes over 100 useful medical tools and calculators, as well as a clinical image case, radiograph and ECG of the week, and over 30,000 images.

Access is free.


Access over 17,000 electronic textbooks.


It has over 90 electronic textbooks and reference books including: Harrison's Principles of Internal Medicine; Hurst’s the Heart; Metabolic and Molecular Bases of Inherited Diseases; the Lange series in the basic medical and clinical sciences; and color atlases of cardiology, dermatology, microbiology, hematology, endoscopy and others.

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