2.4 John Graunt's life table

John Graunt's most important work was to calculate so-called mortality tables - precursors of the present life tables (mortality and survival tables) - from lists of deaths on two time periods. Without knowing anything about probability calculus, he simply counted how many of every one hundred children born were still living. He concluded, for instance, that at the age of six, 64 of the children were alive but at the age of 76 only one. These calculations were the basis for counting mortality rates and they also formed the theoretical background for the present life insurance and pension insurance calculations, for instance.

John Graunt found that per 13 persons born in London 14 persons died, but this ratio was opposite in the countryside. As the population of London increased nevertheless, he concluded it was due to migration from country to town - he was correct in his deduction. Graunt also observed that more boys than girls were born.

In his calculation of the population of London, he came up with an estimate that is considerably lower than that given by his contemporaries. When the population of London was at the time estimated at six to seven million, Graunt proved it to be nearly 384,000. Graunt was right; the population of London did not exceed six million until the 1960s - calculated by modern methods!

Further information about John Graunt's life work can be found at: www.ac.wwu.edu/~stephan/Graunt/.