[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Epidemiology](https://durgical.com/en/epidemiology/) › [Evidence-based medicine](https://durgical.com/en/epidemiology/areas/ebm/) › Evidence-based medicine

# Evidence-based medicine

- Concept

Deciding with the best available evidence, clinical expertise and the patient's values, in five steps.

Updated Nov 5, 2026

## Key points

- Three components: research evidence, clinical expertise and patient values; none is enough alone.
- Five steps: ask (PICO), acquire, appraise critically, apply to the patient and assess performance.
- Evidence is ranked by design and quality: systematic reviews of trials at the top, expert opinion at the bottom.
- Decisions use absolute effects (ARR, NNT, NNH), not only relative ones.
- Absence of evidence of effect is not evidence of absence of effect.

## What it is

Evidence-based medicine (EBM) brings together the best research evidence, clinical expertise and the patient's values and preferences. It is practised in five steps: ask, acquire, appraise, apply and assess. It does not replace clinical judgement: it informs it, and it forces us to think in absolute numbers of benefit and harm.

## Worked example

- Question (made up): in people over 65 with one risk factor, does a preventive treatment versus none reduce stroke over 3 years?
- Search: a systematic review of 5 trials with 12 000 patients in total.
- Appraisal: low risk of bias; stroke at 3 years: 6 % in control and 4 % on treatment.
- ARR = 6 % − 4 % = 2 %; NNT = 1 / 0.02 = 50 patients treated for 3 years to prevent one stroke.
- Harm: major bleeding in 1 % of control and 1.5 % of treated; absolute increase 0.5 %; NNH = 1 / 0.005 = 200.
- Per 1 000 treated: 20 strokes prevented and 5 extra major bleeds.
- Apply: these numbers frame the talk with the patient, who values avoiding a stroke more than the bleeding risk.
- Assess: at 6 months, adherence and events are reviewed to see whether the decision worked in practice.

## The five steps of EBM

| Step | What is done | Tool |
| --- | --- | --- |
| 1. Ask | Turn the doubt into an answerable question | PICO |
| 2. Acquire | Find the best available evidence | Databases, guidelines, systematic reviews |
| 3. Appraise | Judge validity, results and applicability | Critical appraisal, risk of bias, GRADE |
| 4. Apply | Combine with expertise and the patient's values | Shared decision-making |
| 5. Assess | Review the outcome and one's own process | Audit, follow-up |

## Markers

- EBM
- PICO
- NNT
- NNH

## In practice

- Showing benefit and harm per 1 000 people helps shared decisions and avoids the misleading effect of relative percentages.
- Clinical practice guidelines and systematic reviews are shortcuts for step 2: someone has already searched and appraised the evidence.

## Common pitfalls

- Reducing EBM to trials only: expertise and patient values are part of the method.
- Applying a trial result to a patient very different from the participants without thinking about applicability.

## Memory aid

Ask, Acquire, Appraise, Apply, Assess: the evidence enters at step 3, but the decision is made at step 4, with the patient.

## Test yourself

Think of the answer, then tap the question to see it.

## What are the three components of evidence-based medicine?

The best research evidence, clinical expertise and the patient's values and preferences.

## What are the five steps of EBM?

Ask, acquire the evidence, appraise it critically, apply it to the patient and assess the outcome.

## A treatment lowers an event from 6 % to 4 %. What is the NNT?

ARR = 2 %; NNT = 1 / 0.02 = 50 patients treated over the study period.

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## Connections

## Related 6

- [PICO question](https://durgical.com/en/epidemiology/pico-question/)
- [Levels of evidence](https://durgical.com/en/epidemiology/levels-of-evidence/)
- [Critical appraisal of a paper](https://durgical.com/en/epidemiology/critical-appraisal-of-a-paper/)
- [Number needed to treat](https://durgical.com/en/epidemiology/number-needed-to-treat/)
- [Number needed to harm](https://durgical.com/en/epidemiology/number-needed-to-harm/)
- [Clinical practice guidelines](https://durgical.com/en/epidemiology/clinical-practice-guidelines/)

[← All of epidemiology](https://durgical.com/en/epidemiology/)

Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.

Sources: [Chapter 1: Starting a review](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-01) (Cochrane, 2026); [Chapter 14: Completing ‘Summary of findings’ tables and grading the certainty of the evidence](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-14) (Cochrane, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/epidemiology/evidence-based-medicine/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/evidence-based-medicine/