Note on the INFLUENCE of INFANTILE MORTALITY 



ON BIRTH-RATE. 



By G. H. Knibbs, f.s.s., f.r.a.s., etc., 



Commonwealth Statistician. 



[Read be/ore the Royal Society of N. S. Wales, June 1, 1910.] 



This subject was dealt with previously. 1 The measure of 

 the effect of infantile mortality may be thus rigorously 

 determined :— 



Let the total number of births be denoted by B and 

 deaths of infants be denoted by M, and let it also be 

 supposed that the number P of women of child-bearing age 

 in any community is constant, and constantly distributed 

 in the same manner with respect to age, or rather repro- 

 ductivity. Then for the present purpose the birth and 

 infantile mortality rates with respect to this element of 

 the general population may be represented as follows, viz.: 



(1) )8 - BjP 



(2) />■= M/B 



respectively. The rates of infants dyiDg to the women of 

 child-bearing age is thus Pfi. To determine the effect on 

 the birth-rate of any change in the rate of infantile 

 mortality, let the latter be supposed to change to some new 

 value \i = M'/B, M' being the number of deaths and B' the 

 number of births under the changed condition after it has 

 become constant. In both cases the women whose children 

 have died will be added to the number at risk, that is, the 

 number who may increase the number of births. In general 

 however, this risk will be less than that of the remaining 

 women of child-bearing age who have not borne children. 



