single case design
An N-of-1 trial is a crossover trial done within a single individual who receives two or more treatments for periods of time in a particular (usually random) order.
For example, to assess whether an inhaled drug could help a patient with a persistent, dry cough, during some weeks, chosen randomly, the patient would use an inhaler containing a drug; during other weeks the patient would use an identical-looking inhaler which did not contain the drug. The treatment effect is estimated by comparing outcomes (e.g. coughing) in the weeks during which one treatment was allocated to outcomes in the weeks during which the other treatment was allocated.
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