Viewpoint: Do not resurrect the two-stage procedure.

In 1989, Peter Freeman published a paper that challenged a commonly accepted approach for analyzing cross-over trials, the so-called two-stage procedure. Freeman himself recommended using the Bayesian approach of Andy Grieve. The flaws Freeman exposed were serious and led many statisticians to conclude that the procedure was unacceptable. Unfortunately, more than 30 years later, one still encounters its use. This note explains, using a simple simulation, why the two-stage procedure is, indeed, as Freeman showed unacceptable and should not be used.