Evidence-appraisal glossary
N-of-1 trial
An n-of-1 trial is a controlled experiment in a single patient. That one person cycles repeatedly between a treatment and a comparator (often placebo), usually in randomized, blinded order, with outcomes measured in each period, to find which works best for them individually.
Also called: N=1 trial, single-patient trial, single-subject trial.
What it is
An n-of-1 trial turns the study design inward: instead of randomizing many people to different arms, it randomizes the order of treatments over time within one patient. The person repeats several crossover cycles (e.g. drug, then comparator or placebo), ideally blinded, with the same outcome measured in each period. Comparing periods reveals whether the treatment reliably outperforms the alternative for that individual.
How to use it when reading a study
- Scope. Results describe this patient, not a population. An n-of-1 trial answers "does it work for them," not "does it work on average."
- Rigor checks. Look for randomized period order, blinding, washout between periods to avoid carryover, and enough cycles to separate signal from day-to-day fluctuation.
- Best fit. Most credible for chronic, stable conditions with fast-onset, fast-offset treatments and quick, repeatable outcomes.
- Aggregation. Pooling several n-of-1 trials can yield population estimates, but a single one is still a single case.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.