Abstract
This paper addresses an epidemiologic approach to the quantitative evaluation of screening programs for chronic diseases. A new formula is advanced for the quantitative relationship between the yield of a screening program and the natural history of chronic disease, based on the two stage model of disease progression. The formula was applied to follow-up data of the participants and the proportions of cases detected by the screening were estimated as 15.3% for all diseases and 43.8% for hypertensive disorders. The formula is useful for continuous monitoring of ongoing screening programs as well as for potential impact evaluation of hypothetical programs.