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SCIENCE 



[N. S. Vol. LI. No. 1327 



unit. If, on tlie other hand, the percentage 

 is greater than 100 it means that the deaths 

 are more frequent than the births, and that 

 the population is decreasing, again within the 

 specified time unit. The ratio expressed in 

 (i) may be conveniently designated as the 

 vital index of a population. 



were of the births for (a) the 77 non- 

 invaded departments of France; (6) Prussia; 

 and (c) Bavaria; and (d) England and Wales, 

 from 1913 to 1918 by years, with the results 

 shown in Table I. The English data were 

 obtained from the quarterly returns (No. 284) 

 of the registrar-general. 



TABLE I 



Percentage of Deaths to Births 



Pig. 1. Showing the change in the percentage, which deaths were of births in each of the years 1913 

 to 1918 in France (non^nvaded departments) ( ), Prussia ( — — ), Bavaria ( ) and Eng- 

 land and Wales ( — ). 



From the raw data of births and deaths 

 given in the source referred to above I have 

 calculated the percentage which the deaths 



3 This percentage is based upon returns for the 

 first IJhree fourths of the year only. 



These percentages are shown graphically in 

 Fig. 1, together with straight lines fitted to 

 each, by the method of least squares. The 

 equations to the straight lines, where y de- 

 notes death/birth ratio, and x time, are: 



