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A Guide to Health & Medical Research

What information do doctors use when deciding how to treat a patient?

In Evidence Based Medicine (EBM),

Doctors integrate the “best research evidence with clinical expertise and patient values”*

In other words, doctors “[make] a conscientious effort to base clinical decisions on research that is most likely to be free from bias, and using interventions most likely to improve how long or well patients live.”**


*Sackett, D., et al. (2000). Evidence-Based Medicine: How to Practice and Teach EBM, 2nd edition. Edinburgh: Churchill Livingstone, p.1

** Mark H. Ebell, MD, MS, Professor, University of Georgia, Editor-in-Chief, Essential Evidence Plus.

What counts as the “best research evidence” for evidence-based medicine?

The “best evidence” is partially determined by the study type:

  • Experimental studies provide stronger evidence than observational studies;
  • Studies with a large sample size (i.e. that look at a large number of patients) provide stronger evidence than studies with a small sample size.


This Vox article gives a great plain-language description of the various study types in health sciences ⇒


Want to learn to spot all the study designs?

This tutorial from the Centre for Evidence-Based Medicine will help you:

  • Learn to recognize different study types;
  • Understand the advantages and disadvantages of each study design.

Levels of evidence

You’ll often see the levels of evidence for evidence-based medicine represented as a hierarchical pyramid like this one:

This Hierarchy of Evidence Pyramid by Bradley A. Long [author] and Eliza Donne [graphic designer] is shared under a Creative Commons License, Attribution-NonCommercial-ShareAlike 4.0 International.