Cross-over design (cross-over study)

Because each subject serves as their own control, fewer subjects may be needed. The design only works when the effect of the first intervention does not carry over, which is why a washout period may be needed.

A study in which subjects receive a sequence of different interventions (or diagnostic tests). In the simplest case of a cross-over design study, each participant receives either the investigational device or the control in the first period, and the other in the succeeding period. When necessary, the two periods are separated by a suitably long “washout” period to mitigate the effect of the earlier intervention(s). The order in which investigational device or control is given to each subject is usually randomized.

FDA guidance: Design Considerations for Pivotal Clinical Investigations for Medical Devices (November 2013), Section 11, Glossary