On the measurement of hospital case mix.

This article discusses a number of issues related to the measurement of hospital diagnostic case mix. We initially examine a number of previous attempts to measure case mix based on surrogate measures (e.g., facilities and services) and information from predetermined discharge-classification systems. Since a number of researchers have attempted to reduce diagnostic classification data into a single-valued (i.e., scalar) case mix index, we then discuss a number of concepts and assumptions implicit in the construction of such indices. Among these assumptions is the property of functional homogeneity; this property and a methodology baed on Q-type factor analysis for testing for the presence of this property are defined. In order to illustrate the use of the methodology, it is applied to data from 153 hospitals in downstate New York.