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# PICO question

- Concept

PICO turns a clinical doubt into a precise question: patient, intervention, comparison and outcome.

Updated Nov 5, 2026

## Key points

- P: who (age, disease, setting); I: which intervention or exposure; C: compared with what; O: which outcome matters to the patient.
- Sometimes T (time) or S (study design) is added: PICOT, PICOS.
- Therapy or prevention: randomised controlled trial (or a systematic review of trials).
- Diagnosis: cross-sectional study comparing the test with a reference standard in consecutive patients.
- Prognosis: cohort; harm or aetiology: cohort or case-control (for rare effects).

## What it is

A PICO question splits a clinical doubt into four parts: patient or population (P), intervention or exposure (I), comparison (C) and outcome (O). A good question sets what to search for, which studies count and which result to measure. The type of question (therapy, diagnosis, prognosis, harm) points to the design that answers it best.

## Worked example

- Doubt (made up): in children with non-severe pneumonia, are 3 days of antibiotic enough instead of 7?
- P: children aged 2 to 59 months with non-severe community-acquired pneumonia.
- I: 3 days of antibiotic; C: 7 days; O: treatment failure at 14 days.
- Type: a therapy question; the design that answers it: a randomised non-inferiority trial.
- Search using terms for P, I and C: 412 records; 37 pass title and abstract screening; 6 trials are included.
- Share of records that reach the end: 6 / 412 ≈ 1.5 %.
- Reading: without PICO all 412 records would have been read with no criteria; the question set what to include and measure.

## Type of question and the design that answers it best

| Type of question | Example outcome | Preferred design |
| --- | --- | --- |
| Therapy | Mortality, relapse | Randomised controlled trial |
| Diagnosis | Sensitivity, specificity | Cross-sectional against a reference standard |
| Prognosis | Survival, complications | Cohort |
| Harm or aetiology | Adverse event, disease | Cohort; case-control if rare |
| Frequency | Prevalence | Cross-sectional |

## Markers

- P
- I
- C
- O
- PICOT

## In practice

- Writing the PICO question before searching saves time and avoids picking the article that confirms what one already thought.
- The outcome should matter to the patient (death, symptoms, quality of life), not just be a laboratory marker.

## Common pitfalls

- Writing a P that is too broad (adults) or a vague O (improvement): the search returns too much and answers nothing.
- Looking for a trial to answer a prognosis or prevalence question, which other designs answer.

## Memory aid

For whom, what, against what, and for which result? Four short questions build one good long question.

## Test yourself

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

## What does each letter of PICO stand for?

Patient or population, Intervention or exposure, Comparison and Outcome.

## Which design best answers a prognosis question?

A cohort study, which follows patients with the condition over time.

## Which design best answers a question about the accuracy of a diagnostic test?

A cross-sectional study that applies the test and the reference standard to consecutive patients suspected of the disease.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/epidemiology/pico-question/)

## Connections

## Related 5

- [Evidence-based medicine](https://durgical.com/en/epidemiology/evidence-based-medicine/)
- [Study designs: how to tell them apart](https://durgical.com/en/epidemiology/study-designs-how-to-tell-them-apart/)
- [Randomised controlled trial](https://durgical.com/en/epidemiology/randomised-controlled-trial/)
- [Systematic review](https://durgical.com/en/epidemiology/systematic-review/)
- [Levels of evidence](https://durgical.com/en/epidemiology/levels-of-evidence/)

[← 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 3: Defining the criteria for including studies and how they will be grouped for the synthesis](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-03) (Cochrane, 2026); [Chapter 1: Starting a review](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-01) (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/pico-question/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/pico-question/