Definition and Measurement of Senescence 7 



can yet claim causal precedence over any other, and we 

 must therefore try our luck elsewhere. 



The Actuarial Measurement of Senescence 



The actuarial measurement of senescence is based upon 

 the following presupposition: that although senescence is 

 indeed a diverse and complex process, with manifestations 

 in all the structures and activities of the body, its net total 



lOO.OOO 



age in years 



Fig. 1. 



effect is of one measurable kind — to increase vulnerability, 

 the likelihood of dying, as life goes on. 



A measurement of vulnerability is implicit within the 

 information set out in an actuary's life table. A life table 

 may be thought of as a series of figures representing the sur- 

 viving residue, year by year, of a population marked at birth 

 and followed through life until all have died. The table there- 

 fore begins with some arbitrary but large number of indivi- 

 duals (Z^,, say 100,000) and ends at zero when none survive. 

 In the form of a graph, a life table for human beings has the 

 shape illustrated by Fig. 1. 



