vital index

plural vital indexes

1. The ratio of the number of births to the number of deaths in a population over a specific period of time.

   The epidemic of influenza in 1918 was almost exclusively responsible for the decline of the vital index to 36.31% below the figure of 1912.

   1929, Sanders, J., Monograph Series, Issue 1, page 28

   1 more example

   Now what is the real biological meaning of the vital index? What does it actually measure? It measures always the present worth of the evolutionary survival value of a population, but implies nothing as to how this present worth is brought about. Furthermore, the vital index implies nothing intrinsic in a population.

   1926, Sweeney, James Shirtley, The Natural Increase of Mankind, page 26