The search for functions which describe how mortality varies with age is an old one. Over the past two decades demographers have developed model life tables based on the structure of relations among mortalities in different populations rather than explicit expressions of age. The earlier work was analytic and empirical using techniques of statistical regression but more recently functional models have been constructed. These developments are described with particular concentration on the logit relation families of curves.
Some uses of the model life tables in demography are examined such as mortality projections, the dynamics of age structure and estimation from the limited data of developing countries. The implications of the logit system for certain of the “classic” speculations are considered—the span of life, whether a generation carries its own mortality with it and the accumulation of the unhealthy at older ages with saving of life at the younger.