938 G. H. KNIBBS. 
On THE INFLUENCH oF INFANTILE MORTALITY on 
BIRTHRATE. 
By G. H. KNIBBS, F.S.S., F.R.A.S.. Commonwealth 
Statistician. 
[Read before the Royal Society of N. S. Wales, October 7, 1508. | 
1. A general survey of the vital statistics of any country 
discloses the fact that, on the whole, with an increase of 
infantile mortality there is an increase of birth-rate. These 
rates are ordinarily measured as follows:— 
Denoting the average total population during the period 
under review by P, the total number of births during the 
same period by B, and the total number of infants dying by 
M, the birthrate denoted by (, is B/P; and similarly the 
rate of infantile mortality denoted by p, is M/B, since it is 
the ratio of the number dying to the total number born in 
the period. 
In order to make strictly comparable the results at 
different periods and of populations differently constituted 
in respect of sex and age, the birthrates should be referred 
to the number of women of childbearing age, and so stan- 
dardised as to express uniformity in respect of natural 
fecundity or fertility. If, however, the constitutions of 
populations are sensibly identical in regard to sex and age, 
the corrections necessary are smalland may for the present 
purpose be disregarded. 
2. Suppose that » be taken as the independent variable, 
and the mean of a group of values of £ be formed for the 
corresponding small ranges of values of ». The result 
would be what may be called a mean birthrate By say, 
related toa mean rate of infantile mortality, +n say these 
