Modelling the reciprocal of the survivorship function

In a recent study by Mitra [1], Brassʹs model of linear relationship between the logits of the life table survivorship function l(x) of any two life tables was transformed to a similar relationship between the reciprocals of l(x). It has been shown in the current paper that such a relationship implies strong correlation between the reciprocals of l(x) and l(y) where x and y are any two ages and that this correlation increases as the age difference decreases in absolute value. Two factors emerged when this correlation matrix for each sex was subjected to principal components analysis. They explained 98 percent of the variation and as a result turned out to be excellent predictors of life tables in general and of comprehensive measures of mortality such as life expectancy in particular. In fact, the factor scores corresponding to the two principal components, for any life table or for any country, can be treated as measures of mortality along two independent dimensions labeled, in this paper, as acquired-immunity and senescence.