Index of endemicity.

The author discusses the difficulties involved in defining the term "endemicity", and suggests a new approach to the problem-namely, the establishment of indices of endemicity, based on such data as are usually collected by national health administrations (mortality and morbidity rates, spleen-rates, case incidence in seaports, etc.). Examples are given of the calculation of the endemicity index for a number of diseases from different types of data obtained from various countries. An important advantage of the endemicity index is that it provides an easy means of studying the geographical pattern of endemic foci of disease.