[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Epidemiology](https://durgical.com/en/epidemiology/) › [Study designs](https://durgical.com/en/epidemiology/areas/designs/) › N-of-1 trial

# N-of-1 trial

- Study design

A trial in a single patient: two treatments alternate several times, in random order, to find out which works better for that person.

Updated Nov 13, 2026

## Key points

- Repeated crossover in one patient: several pairs of A and B periods.
- Random order within each pair; blinding with identical-looking preparations if possible.
- Chronic, stable condition; effect that starts and stops quickly.
- The result applies to that patient; several N-of-1 trials can be pooled in a meta-analysis.
- Outcome reported by the patient (symptoms, sleep, pain) on a fixed scale.

On this page

- The basics Key points
- What it is
- How it is built
- Worked example
- N-of-1 trial versus other ways of deciding
- Markers
- When to use it
- Common pitfalls
- Memory aid

- Study Test yourself

- Connections Connections

## What it is

An N-of-1 trial is a repeated crossover trial in one person: two treatments (or treatment and placebo) alternate over several pairs of periods, with the order in each pair randomised and, when possible, blinded. It answers an individual question: which option helps this patient more. It only works in chronic, stable conditions, with treatments whose effect starts quickly and fades soon after stopping.

## How it is built

- Patient and clinician agree on the question and the outcome that matters (for example, pain from 0 to 10 points).
- Three or more pairs of periods are planned, with washout if needed.
- In each pair the order of A and B is drawn at random.
- The patient records the outcome in each period.
- A and B periods are compared within each pair and overall.

## Worked example

- A patient with stable knee osteoarthritis compares two analgesics, A and B, over 3 pairs of 2-week periods in random order.
- Mean pain (0 to 10 points): pair 1 A 4, B 6; pair 2 A 5, B 5; pair 3 A 3, B 6.
- Differences B − A: 2, 0 and 3 points; mean = (2 + 0 + 3) / 3 = 1.67, rounded to 1.7 points in favour of A.
- A was better in 2 of the 3 pairs and worse in none.
- Reading: for this patient, A lowers pain about 1.7 points more than B; with the clinician, they decide to continue A.

## N-of-1 trial versus other ways of deciding

| Aspect | N-of-1 trial | Classic crossover trial | Usual trial and error |
| --- | --- | --- | --- |
| Patients | One | Several, one crossover each | One |
| Repetitions | Several A/B pairs | One A/B pair | None planned |
| Random order | Yes, in each pair | Yes | No |
| Question | What helps this patient? | What helps on average? | Clinical impression |
| Bias | Low if blinded | Low | Expectation and regression to the mean |

## Markers

- N-of-1
- Paired periods
- Washout

## When to use it

- Chronic pain, insomnia, stable asthma, symptoms of rare diseases with no large trials.
- When group evidence does not fit the patient well, or a long-term treatment is in doubt.
- Useful for deciding, on evidence, to stop a treatment that may no longer help.

## Common pitfalls

- Using it in conditions that change fast or resolve.
- Long-acting treatments without enough washout: carry-over mixes the periods.
- Running a single pair of periods: the effect cannot be told apart from chance or natural variation.

## Memory aid

N-of-1: the patient is the whole trial; they cross over several times so chance does not decide for them.

## Test yourself

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

## What must a condition be like for an N-of-1 trial?

Chronic and stable, with a treatment whose effect starts quickly and fades soon after stopping.

## Why are several pairs of periods repeated?

To tell the treatment effect apart from natural variation and chance.

## To whom does the result of an N-of-1 trial apply?

To the patient studied; only by pooling many N-of-1 trials can an average effect be estimated.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/epidemiology/n-of-1-trial/)

## Connections

## Related 4

- [Crossover trial](https://durgical.com/en/epidemiology/crossover-trial/)
- [Randomised controlled trial](https://durgical.com/en/epidemiology/randomised-controlled-trial/)
- [Blinding](https://durgical.com/en/epidemiology/blinding/)
- [Statistical vs clinical significance](https://durgical.com/en/epidemiology/statistical-vs-clinical-significance/)

[← 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 23: Including variants on randomized trials](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-23) (Cochrane, 2024); [Chapter 8: Assessing risk of bias in a randomized trial](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-08) (Cochrane, 2024).

## **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.

---
Source: https://durgical.com/en/epidemiology/n-of-1-trial/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/n-of-1-trial/