The ecologic method in the study of environmental health. I. Overview of the method.

This paper summarizes the salient features of the ecologic method, with emphasis on its application in the study of environmental health. Various types of ecologic design are described, with examples. Finally, the main advantages and disadvantages are indicated. A companion paper discusses the methodology of ecologic designs in more detail and describes a census of data sets with potential suitability for the ecologic study of water quality and human health.