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Evidence-Based Medicine: Using EBM Effectively

How to Read a Paper series


Dr. Trisha Greenhalgh is a British physician and professor of medicine that wrote a series of excellent articles in the mid to late 1990's as the idea of finding, analyzing and using Best-Evidence from the literature was gaining in importance and prominence.  Although over 10 year old, her "How to Read a Paper" series of articles, published in the BMJ, still offer valid insight into increasing critical appraisal skills.  NOTE: SOME OF THESE ARTICLES BEGIN ON PAGE 2 OR 3 OF THE LINKED PDF FILE.

Greenhalgh, T. (1997). How to read a paper. getting your bearings (deciding what the paper is about). BMJ (Clinical Research Ed.), 315(7102), 243-246.

Greenhalgh, T. (1997). How to read a paper. papers that report diagnostic or screening tests. BMJ (Clinical Research Ed.), 315(7107), 540-543.

Greenhalgh, T. (1997). How to read a paper. papers that report drug trials. BMJ (Clinical Research Ed.), 315(7106), 480-483.

Greenhalgh, T. (1997). How to read a paper. statistics for the non-statistician. I: Different types of data need different statistical tests. BMJ (Clinical Research Ed.), 315(7104), 364-366.

Greenhalgh, T. (1997). How to read a paper. statistics for the non-statistician. II: "significant" relations and their pitfalls. BMJ (Clinical Research Ed.), 315(7105), 422-425.

Greenhalgh, T. (1997). How to read a paper. the medline database. BMJ (Clinical Research Ed.), 315(7101), 180-183.


How to read a paper: the basics of evidence-based medicine - Trisha Greenhalgh

ISBN: 9781444334364

The 5 A's

Using EBM effectively takes more than understanding how to interpret outcomes from something you read. It involves knowing the right question to ask, turning that question into a good search, knowing the best place to look, finding what is available and then using the evidence you find in the care of your patient. Use the "5 A's" as a step-by-step guide to locate best evidence.

  1. Assess
    • Identify the clinical problem. What is it you want to know?
  2. Ask
    • Use the PICO formula to create a good question:
      • P=PATIENT – Who is your patient?
      • I=INTERVENTION – Are you looking to diagnose? Treat? Learn about a prognosis?
      • C=COMPARISON – Is there a control? Placebo? A "gold standard"?
      • O=OUTCOME – What do you hope to accomplish? Better/best treatment? Decreased mortality?
    • A good PICO might read "In an 86-year old man with coronary artery disease, is aspirin a more effective agent than heparin in reducing risk of stroke?"
  3. Acquire
    • Use your PICO formula to search for good evidence. Start your search using only two to three terms - you can always add more. Use the information resources on the EBM home page as a starting point.
  4. Appraise
    • What have you found? Where did you find it? Are the results significant to your patient? How strong is the evidence? Are there any confounding variables such as bias present?
  5. Apply
    • Now apply and discuss the evidence you have found with your patient.

You say PICO, I say PICOTT

The PICO mnemonic, essential for formulating a good Evidence-Based questions, is usually seen written as PICO but sometimes shows up as PICOTT as well?  What is the difference.  As shown above, the standard elements of PICO are Patient, Intervention (or Index for a diagnostic question), Comparison or Control and Outcome.  But at times, one or even two T's may be added.  The T's stand for:

  • Type of question being asked - e.g., therapy / diagnosis / etiology / harm / prognosis / prevention. 
  • Type of study being sought to answer the question - e.g., RCT / Systematic Review / Cohort Study
  • Time - e.g. would the desired outcome be realized in 1 month, 1 year, 10 years, etc.

Grading Evidence

There are a number of rating scales that are used to define "best evidence".  Visit this page on the Essential Evidence Plus web site to learn about the four most common scales (Centre for EBM Oxford, SORT, GRADE and Practice Guidelines).