Written by Ronny Gunnarsson and first published on April 30, 2015.
Last revised on March 22, 2020.

You must cite this article if you use its information in other circumstances. An example of citing this article is:
Ronny Gunnarsson. Evidence Based Medicine [in Science Network TV]. Available at: https://science-network.tv/evidence-based-medicine/. Accessed July 27, 2024.

Suggested pre-reading	What this web page adds
Introduction to research Introduction to statistics 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.)

Table of Contents (with links)

The five steps in Evidence Based Medicine

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

PICO

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):

Level	Trustworthiness	Study design
I	Very low risk for bias (and incorrect conclusions)	– Systematic review with meta analysis of high quality Randomized Clinical Trials (RCT)
II	Low risk for bias (and incorrect conclusions)	– High quality Randomized Clinical Trial (RCT)
III-1	Some potential for bias (and incorrect conclusions)	Low quality Randomized Clinical Trial (RCT)
III-2	Clear potential for bias (and incorrect conclusions)	– Controlled Clinical trial (CCT) – Cohort study – Case-Control Study
III-3	Considerable potential for bias (and incorrect conclusions)	– Multiple Single Case Research Experimental Design – SCRED – Historic cohort study – Cross-sectional studies – Ecological studies
IV	May 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

Relevant study population?
Publication bias?
Studies described well enough?
Sensible scoring – evaluation? (such as blinding)
Extracting the right data?
Managing conflict of interest?
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

Analysis of Funnel plots

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Evidence Based Medicine