428 
STATISTICS: R. PEARL 
Proc. N. a. S. 
statistical purposes, be entirely removed by adopting as an age-consti- 
tution index the function 
4> = s|A'j.(M-M,) (2) 
where 5, A and P have the same significance as before, and M = mean 
age of living population in any community, Mp = mean age of persons 
in a stationary population unaffected by migration and which, assuming 
I ALBANY 
Lr POPULATION 
I 
/5 
25 
45 
/\GE 
65 
35 
Fig. 1. Diagram showing age distribution of population, grouped in six age classes. 
The last class in this and other diagrams is assumed to have its ending at age 95. 
The solid line gives the stationary life table population, and the broken line the 
population of Albany. Total area under each curve = 100%. 
the mortality rates of Glover's Life Table, would result if 100,000 persons 
were born alive uniformly throughout each year (ikf^ calculated from 
L, Hne of Glover's Table (p. 16) = 33.796 years). 
This procedure simply multiplies our former index by the diff"erence 
(given its proper sign) between the mean age of the observed population 
and the mean age of the standard population on the basis of which 
was calculated. Since in fact the mean age of any actual urban popula- 
tion is never likely to be as great as the mean age of the stationary popula- 
