Methods of smoothing mortality tables have long been of interest to actuaries. Early methods were primarily nonparametric, although de Moivre (1724) found a uniform distribution to be useful over short time periods and other parametric methods were occasionally suggested. The first parametric family to gain wide attention was that of Gompertz (1825). This family was extended with the addition of a parameter by Makeham (1860), and subsequently by various other authors. An historical review of considerable interest has been given by Ogborn (1953).