Methods for projecting the incidence and prevalence of chronic diseases inageing populations: application to Alzheimer's disease

Projections of the incidence and prevalence of disease are important for pu blic health planning. This paper describes methods for projecting the incid ence and prevalence of a chronic disease in ageing populations. The approac h uses age-specific disease incidence rates together with assumptions about survival to reconstruct disease prevalence. The methods can be used to eva luate the potential impact of public health interventions that may prevent disease or prolong survival. We used the methods to project the future prev alence of Alzheimer's disease in the United States. We found that the preva lence of Alzheimer's disease will nearly quadruple over the next 50 years. Although projections of the absolute prevalence are sensitive to assumption s about the age-specific incidence rates of disease, the proportionate grow th is relatively insensitive. The increase in prevalence results from the a geing of the U.S. population. In order to perform the calculations, we have assembled U.S. Census population projections and U.S, mortality rates into computer software that is available from the authors at www.jhsph.edu/Depa rtments/Biostats/software.html. Copyright (C) 2000 John Wiley & Sons, Ltd.