Methodological comments: McFarlane et al

Abstract

Does the McFarlane et al study provide a model for practical trials? Unfortunately, not. The methodological problems are here reviewed and used as a springboard to set out methodological criteria that might define such a model.

Keywords: criteria; methodology; practical trials.

Fig. 1.

Three hypothetical situations with solid lines indicating the true outcome curves for T and C as a function of the selected baseline variable, the dotted lines indicate extrapolations that would be used with the parallel line assumption. The vertical axis is the outcome and the horizontal axis the baseline factor used for assignment (cutpoint here at 50). Only the right side (baseline over 50 here) of the T response curve and the left side of the C response curve are actually observed. The vertical separation of the dotted lines indicates the estimated treatment effect size using this design. The separation between the solid lines indicates the true treatment effect, which may not be the same for patients with differing baselines.