Mapping mortality and morbidity patterns: an international comparison.

A set of 49 national, intranational and international health atlases was surveyed to characterize their mapping methodology with respect to the populations covered, the diseases represented, the mapping techniques, and statistical methods. Little consistency was found concerning the choice of data function to be mapped, minimum event frequency requirements, method of age standardization, or map colour systems. Many atlases did not include basic epidemiological information; for instance, approximately half the atlases did not quote population denominators. There was a tendency to emphasize statistical significance over rate values, and to focus on high rather than low risk. Very few atlases included supplemental information on environmental factors. Most adopted a descriptive stance, and attempted no aetiological interpretation. We conclude that inter-atlas comparisons are made very difficult by methodological differences, and that even regional comparisons within atlases should be made cautiously. We propose a set of methodological guidelines for consideration in future atlases.