A Population with Continually Declining Mortality

Robert Schoen, Pennsylvania State University
Stefan H. Jonsson, Pennsylvania State University
Paula Tufis, Pennsylvania State University

Many countries have recently experienced sustained declines in mortality, and the paper presents a new model for analyzing such declines. Every year there is one birth in the model. Mortality increases exponentially over age at rate b, while decreasing exponentially over time at rate c. The model population is strikingly linear in its behavior over time. The size of the population is virtually the same as its average age at death, and both increase annually by c/b. Period life expectancy also increases linearly by c/b, while the average age of the population increases by c/(2b). Preserving a constant ratio of persons in the economically active ages to those in the retirement ages implies an increase in the "normal" age of retirement of about 6.8c years per year. The ability to accommodate varying rates of decline and the linearity of the changes enhance the model's potential for analyzing steadily increasing longevity.