CHANGES WITH AGING 431 



(1) LogY = a + b(X-100) +c(Z),and 



(2) Log(probitY)=e + f(X-100) + g(Z), 



in which Y is the frequency (%) of severe atherosclerosis and X is the 

 mean cholesterol concentration over the period from decade 1.5 to 

 decade Z. 



The solutions to equations 1 and 2 are given in Table IV, together 

 with the observed and estimated \alues of Y. The correspondence be- 

 tween the observed and the predicted frequencies of severe athero- 

 sclerosis is reasonably good with both equations. It seems reasonable to 

 conclude that these two parameters of age and serum-cholesterol con- 

 centration are probably the major factors in determining the develop- 

 ment of severe atherosclerosis. > 



TABLE IV 



Atherosclerosis vs. Age and Serum Cholesterol 



Y = % grades 3 + 4 atherosclerosis ■ . . 



X = Cumulative mean cholesterol, mg. per 100 ml. 

 Z = Age in decades —1.5 ... . 



(1) Log Y = -0.57 + 0.013 (X-100) + 0.23 Z 



(2) Log (probit Y) = 0.30 + 0.0024 (X-100) + 0.042 Z ' 



Observed , Estimated from 



Value Y ' (1) (2) ' / 



7. L5 



3 •., .. 



7 



18 <c 



40 

 72 



The log probit form ( equation 2 ) has the advantage that the pre- 

 dicted values will always sta\' within the limits of and 100 per cent. It 

 is interesting to see the implications of equation 2 for other ages and 

 mean serum-cholesterol levels. These are summarized in Figure 7. With 

 a mean cholesterol lexel of 100 mg. per 100 ml. over all the years, even 

 at age 75 the prediction is that only 7 per cent of the men would have 

 severe coronary atherosclerosis. And with a mean cholesterol level of 

 300 over all the years to age 35, the equation indicates that 99 per cent 

 of such men, will ha\e severe atherosclerosis by that age. - ,.., 



This is all very well, but what is the implication, if an\', for the 

 problem of aging? The point is that if atherosclerosis is a major phe- 



