Fixed-effect versus random-effect models for evaluating therapeutic preferences.

A preference trial is a special form of cross-over trial where clinical conditions determine when patients change treatment, in a prescribed order. This leads to binary responses with variable lengths. In cross-over trials with normal responses, patient effect may be treated as either fixed or random. However, with binary responses, random- and fixed-effect assumptions may lead to very different conclusions, so that one is no longer an alternative to the other. Copyright 2002 John Wiley & Sons, Ltd.