Evidence-appraisal glossary
Crossover trial
A randomized trial in which each participant receives two or more treatments in sequence, so each person serves as their own control. The order of treatments is randomized.
Also called: crossover study, cross-over trial.
Because each participant is compared against themselves, crossover trials remove between-person variation and can reach useful conclusions with fewer people. They suit chronic, stable conditions where treatment can be started and stopped, such as pain or asthma. The main pitfall is a carryover effect, where the first treatment still influences the person during the second period; a washout gap between periods is used to limit this, and the design does not fit conditions that resolve or change over time.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.