Professional Description:
"A method of comparing two (or more) treatments or interventions in which subjects, upon completion of one treatment, are switched to the other. In the case of two treatments, A and B, half the patients are randomly allocated to receive these in the order “A first, then B,” and half to receive them in the order “B first, then A"."
Source: JAMA evidence. American Medical Association; 2014 Jun. Available from: http://www.jamaevidence.com/glossary