Potential pitfalls in interpreting maps of stabilized rates.

There have been many advances in the mapping of disease mortality and morbidity rates in recent years. An increasingly common approach is to calculate "stabilized" rates for individual geographic areas by incorporating information from the entire set of data. One such method, adopted by the Environmental Protection Agency [corrected] for its mortality maps, is described and applied to national end-stage renal disease data. Some possible difficulties in interpretation are noted, resulting from: (1) insufficient shrinkage, (2) highly skewed rate distributions, (3) different denominator distributions, and (4) variations in population density.