Epidemiologic models in studies of vectorborne diseases.

THE CENTEE of interest and point of em¬ phasis of any living subject changes. The center of active interest in epidemiology gravi¬ tates to the United States of America, and I pay homage to the outstanding quality and volume of work I have seen in this country. It is therefore a unique privilege to give the Dyer Lecture at the National Institutes of Health, and especially to do so in the presence of Dr. Eolla E. Dyer, who is largely responsible for the stature of the Institutes and after whom the lecture is named. An epidemiologic model is a closely argued statement of the quantitative aspects of trans¬ mission of a disease. This model includes all those factors with a direct influence on the dynamics of transmission and shows propor¬ tionately, but not necessarily in exact numerical terms, how changes in any one or all of the fac¬ tors will influence transmission, incidence, and prevalence. The model taken by itself has no significance; it proves nothing and explains nothing, except perhaps the mind of the man who made it. Its value lies in its potential use as a tool for understanding the patterns in which the dis¬ ease occurs, the causes of divergence between them and of fluctuations in prevalence, the rel-