Clinical research & EBM · Reference
What is evidence-based medicine?
Evidence-based medicine is an approach that integrates the best available research evidence with clinical expertise and patient values to inform decisions. Defined by David Sackett and colleagues, it provides a framework — often summarised as the five As — for using evidence systematically.
The three pillars
As defined by Sackett and colleagues in the 1990s, evidence-based medicine rests on integrating three elements: the best available research evidence, clinical expertise, and patient values and preferences. None is sufficient alone — evidence informs but does not replace judgement, and judgement must be exercised with the patient’s circumstances and wishes in view. EBM emerged as a movement to make decisions more explicitly grounded in research, drawing on tools such as the evidence hierarchy and the randomized controlled trial. As a CASRAI definition, this describes the framework, not clinical guidance.
The five As
EBM is commonly taught as a sequence of steps, the "five As". Ask: convert an information need into an answerable question, often using PICO. Acquire: search efficiently for the best evidence. Appraise: critically appraise that evidence for validity, effect size and applicability. Apply: integrate the appraisal with expertise and the individual’s values. Assess: evaluate the outcome of the process and seek to improve it. (Earlier formulations used four As, before "Assess" was added.) This cycle frames EBM as a reproducible, teachable process rather than an appeal to authority.
Evidence synthesis and appraisal
EBM places particular weight on synthesised evidence — systematic reviews and meta-analyses — because they pool findings and reduce the influence of any single study. Reporting standards such as PRISMA and conduct guidance from bodies such as Cochrane support this. Modern EBM also stresses grading the certainty of evidence, for example through GRADE, and distinguishing the quality of evidence from the strength of a recommendation. The result is a discipline focused on how to find, appraise and use evidence transparently.
Key facts
At a glance
- Defined by: David Sackett and colleagues (1990s)
- Three pillars: Best evidence, clinical expertise, patient values
- Process: The five As — Ask, Acquire, Appraise, Apply, Assess
- Relies on: Systematic reviews and the evidence hierarchy
- Grading: Certainty assessed via frameworks such as GRADE
Common questions
FAQ
Who defined evidence-based medicine?+
Evidence-based medicine was defined in the 1990s by David Sackett and colleagues as the conscientious, explicit and judicious use of current best evidence in decision-making. Their definition integrates research evidence with clinical expertise and patient values.
What are the five As of EBM?+
The five As are Ask, Acquire, Appraise, Apply and Assess — converting a need into a question, searching for evidence, critically appraising it, integrating it with expertise and values, and evaluating the outcome. Earlier versions used four As before Assess was added.
Does evidence-based medicine mean following research blindly?+
No. EBM integrates the best research evidence with clinical expertise and patient values; evidence informs but does not replace judgement. It is a framework for using evidence systematically, not a rule to apply research without regard to context.
The step most authors miss
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