Cross-over study

In epidemiology, cross-over studies or crossover trials are a type of randomized controlled trial. Cross-over studies are "studies comparing two or more treatments or interventions in which the subjects or patients, upon completion of the course of one treatment, are switched to another. In the case of two treatments, A and B, half the subjects are randomly allocated to receive these in the order A, B and half to receive them in the order B, A. A criticism of this design is that effects of the first treatment may carry over into the period when the second is given."

The results of crossover studies "tend to agree with those of parallel arm trials, although there was a trend for more conservative treatment effect estimates in parallel arm trials".

Variations on the standard AB, BA design have been proposed.