ABSTRACT
This chapter is written for (health) economists interested in the conceptualization and measurement of ageing in demography, biology, and gerontology. I review two alternative methods to measure ageing and a theory that explains the outcome of both of these measurements. I explain how ageing, conceptualized as increasing probability of death, can be accurately and conveniently expressed by the Gompertz-Makeham law. I discuss the stability of the estimated parameters, inferences about human lifespan, and similarities and differences of ageing across sexes and countries and over time. Alternatively, ageing can be measured as accumulation of health deficits. The chapter reviews the frailty index, designed to measure biological ageing, and demonstrates important similarities and differences between the force of mortality and the accumulation of health deficits. Regularities of health deficit accumulation across individuals, at the level of (sub) populations, and across the world are discussed. The chapter also introduces reliability theory and shows how increasing mortality and frailty can be explained as a stochastic process of loss of built-in redundancy of organisms. The chapter concludes with some suggestions for the modeling of health and mortality in economics.
