Evidence Based Medicine

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Ronny Gunnarsson. Evidence Based Medicine [in Science Network TV]. Available at: https://science-network.tv/evidence-based-medicine/. Accessed July 13, 2020.
Suggested pre-reading What this web page adds
  1. Introduction to research
  2. Introduction to statistics
  3. Study design
This web-page describes what evidence based medicine is. Reading this will give you an understanding of the concept and make it easier to read publications presenting evidence.

(This page is still under construction. Sorry for the inconvenience.)

The five steps in Evidence Based Medicine

  1. Define questions and level of evidence
  2. Systematic retrieval of publications
  3. Critical appraisal of evidence – If possible a meta-analysis
  4. Apply results in clinical practice
  5. Evaluate performance in clinical practice


One goal of Evidence Based Medicine (EBM) is to collect scientific evidence for common clinical questions. The best way to do this is to ask the right questions. Sackett first suggested a framework for how to come up with well defined and answerable questions .  The framework says each question should be structured in the PICO format; Patient or Problem, Intervention, Comparison, Outcome/s. The following video describes (in a funny way) evidence based medicine and PICO:

The PICO format is perfect for clinical questions around choice of therapy (where no therapy might be one of available choices). However, the PICO framework is less suitable for questions other than around choice of therapy .

In conclusion, strive to use the PICO format if your question is about choice of therapy. For other questions use suitable parts of the PICO framework. There might also be questions where all parts of the PICO framework, at least as conventionally described, are unsuitable.  Hence, be aware of the PICO framework but only refer to it if it helps in your situation. Don’t try to squeeze everything into the PICO framework.

Possible aims with a Meta-analysis

  • Show effect that single studies can’t (Forrest plots)
  • Show more studies not needed
  • Explain why studies give different results.

(This section is still under construction. Sorry for the inconvenience.)

The staircase of evidence

Some study designs are more reliable than others in proving that a specific treatment is effective (or proving cause and effect):

LevelTrustworthinessStudy design
IVery low risk for bias (and incorrect conclusions)– Systematic review with meta analysis of high quality Randomized Clinical Trials (RCT)
IILow risk for bias (and incorrect conclusions)– High quality Randomized Clinical Trial (RCT)
III-1Some potential for bias (and incorrect conclusions)Low quality Randomized Clinical Trial (RCT)
III-2Clear potential for bias (and incorrect conclusions)– Controlled Clinical trial (CCT)
– Cohort study
– Case-Control Study
III-3Considerable potential for bias (and incorrect conclusions)– Multiple Single Case Research Experimental Design – SCRED
– Historic cohort study
– Cross-sectional studies
– Ecological studies
IVMay provide ideas but does not prove anything– One Single Case Research Experimental Design – SCRED
– Case studies / case series

There may of course be studies within each level of trustworthiness being of very good or very poor quality. Hence, a very good controlled clinical trial might be more trustworthy than a very poor quality RCT. However, as a general rule most randomized controlled trials are more trustworthy than most controlled clinical trials.

Potential problems with EBM

  1. Relevant study population?
  2. Publication bias?
  3. Studies described well enough?
  4. Sensible scoring – evaluation? (such as blinding)
  5. Extracting the right data?
  6. Managing conflict of interest?
  7. Presenting findings appropriately?

Do we have to require randomized controlled trials for everything  ?

(This section is still under construction. Sorry for the inconvenience.)

Useful links


Akobeng AK. Principles of evidence based medicine. Archives of Disease in Childhood [Internet]. 2005 Aug 1 [cited 2019 Jan 22];90(8):837–40. Available from: https://adc.bmj.com/content/90/8/837
Huang X, Lin J, Demner-Fushman D. Evaluation of PICO as a Knowledge Representation for Clinical Questions. AMIA Annu Symp Proc [Internet]. 2006 [cited 2019 Jan 22];2006:359–63. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1839740/
Smith GCS, Pell JP. Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ [Internet]. 2003 Dec 18 [cited 2016 Oct 18];327(7429):1459–61. Available from: http://www.bmj.com/content/327/7429/1459

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