Should we cross off the crossover? [editorial]

Should we cross off the crossover?The simple two-treatment, two-period crossover trial is under attack again.In ideal circumstances this design provides an efficient way of comparing the efficacies of two treatments for the short-term alleviation of a chronic condition.Subjects receive the treatments during two periods of administration separated by a wash-out period intended to remove any possible carry-over effect.The two orders of administration, AB and BA, are assigned to subjects at random.Twofeaturesof the design account for its popularity.By enabling each subject to provide