Definition and Measurement of Senescence 



The difficulties and covert implications of such a scheme of 

 measurement may now be commented upon one by one. 



(1) In the first place, senescence is a process. At their face 

 value, the life table and its derivatives record, not a sequence 

 of events which takes place in the lifetime of a single indivi- 

 dual, but the age-frequency distribution in the population 

 as a whole of a single event in life, viz: death, its end. 



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This is not a weighty criticism. It is a well understood 

 convention that, with certain safeguards, the frequency of 

 the occurrence of an event in a population can be taken to 

 represent the probability of its happening to an individual. 

 If these safeguards are observed (not all can be: see below) 

 we can legitimately claim to be measuring that change in an 

 individual's lifetime which makes him progressively more 

 vulnerable to mortal hazards. 



(2) The use of the force of mortality assumes that all death 

 is accidental in origin (using the word "accidental" in its 



