74 
STATISTICS: PEARL AND BURGER Proc. N. A. S. 
the trend feasible within the space of a single printed page, the data have 
been combined in quinquennial periods in table 2. In this table are 
given, for each 5 year period, the total births, total deaths, vital index, 
and crude birth rate. The latter figures have been calculated directly 
from the birth and population figures and differ slightly (but in no wise 
significantly) from the crude birth rates given in Annual Reports of the 
Registrar-General, chiefly because of the fact that we have used a different 
quinquennial grouping. 
INFLUENZA 
INFLUENZA 
WAI^ AND 
INFLUENZA 
BIRTH RATE 
mo 45 50 55 60 65 70 75 60 85 90 95 BOO 05 10 15 ZO 
FIG. 1 
Trend of vital index (100 births/deaths) and crude birth rate in England and Wales, 1838-1920, inclusive 
The vital index and birth rate data from table 2 are shown graphically 
in figure 1. 
The diagram is plotted on an arithlog grid, in order that the slopes of 
the lines may be strictly comparable.^ 
It is at once apparent that the ratio of births to deaths in England and 
Wales had a slow hut extremely even and steady increase from 1838 to IQ14. 
This steady progress was interrupted to a degree sufficient to be apparent 
