Actuarial Aspects of Human Lifespans 11 



distribution of lifespan in humans then it appears possible 

 that over and above the large increase in ability to attain the 

 allotted span, the modal span itself is slowly increasing. Even 

 in 1841 there had been a "break through" of the barrier of 

 three score and ten. Women can now talk modestly of "four 

 scores". 



Comparison between men and women 



If the proportion of all deaths which are senescent can be 

 used as a measure of ability to survive the allotted term of 

 life, then the improvement in the mortality of women as 

 compared with that of men appears more as a greater shift in 

 the optimum than as a greater improvement in attainment. 

 The advantage of women over men (or conversely the dis- 

 advantage of men as compared with women) is thus a very 

 general one and calls for intense examination. 



Other aspects for examination 



It would be possible to forecast mortality not only by 

 examining the medical and environmental possibilities for the 

 reduction of anticipated deaths as Clarke suggested but also 

 by predicting the further change in the parameters shown in 

 the table. It is tempting for example to suggest that the 

 national life-table in 1970-72 will show for men a modal span 

 of almost 77 and an attainment of natural senescence by 78 

 per cent, but this kind of temptation will be pursued else- 

 where. 



Another possibility is that the "attainment" proportion 

 (i.e. ratio of senescent deaths to all deaths) might be used as a 

 mortality index for international comparison. This also is 

 outside the present discussion. 



The limitations of the life -table 



The life-table as normally computed is based on the rates of 

 mortality experienced by the population of all ages as they 



