REEXAMINATION OF PROPRIETY OF THE CROSSOVER DESIGNS

Yamamoto Seishi, Tasaki Takenobu, Goto Masashi

doi:10.20551/jscswabun.5.1_1

In this paper, we reexamine the propriety of the crossover designs by applying them to clinical trials, focusing on the two-treatment, two-period crossover trials which test two treatments (or drugs) at two periods. Specifically, we present a pedigree of pros and cons to the crossover designs. Then, we call forth your attention to preparation of wash-out period between 1st and 2nd periods, invasion of treatment to patients' mental state (masking of treatment), temporal change of response level (indices to be evaluated) and balance in allocation of patients to treatment order groups, considering the problems due to carryover effects that are so to speak the Achilles' tendon of the crossover designs. In case where carryover effects were detected at the analysis stage of the crossover trials, we tried the transformation of observed response as an expost facto remedy. We actually reanalyzed five sets of data from published literature using power-transformation and ACE-transformation. As a result, it was suggested that carryover effects were rarely eliminated by the data transformation. Thus, in the application of the crossover design, preexamination at the designing stages is especially important. Finally, we describe the fields of clinical trials where the crossover trials are used in relatively high frequency.

REEXAMINATION OF PROPRIETY OF THE CROSSOVER DESIGNS

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