A simple measure in defining optimal strata in clinical trials.

This paper deals with balancing groups with respect to prognostic factors in clinical trials, as a means of increasing the power of a study. We use the Mantel-Haenszel statistic to obtain a simple measure for assessing the relative efficiency of different factors for stratification and to find optimal cutpoints for the given factors. For any available database, the measure can be used to construct optimal strata for a clinical trial. The paper also presents a practical approach for reducing the number of strata using discriminant regions with a method of assessing the effectiveness of this approach. An example from a large database of severe head trauma patients illustrates the utility of the measure.