What is John Graunt contribution to demography?

John Graunt is known as the father of demography for his work in applying statistical methods to study population data. His book "Natural and Political Observations Made upon the Bills of Mortality" published in 1662 is considered a seminal work in the field of demography. Graunt's analysis of population data laid the foundation for the field of modern demography by introducing the use of numerical data and statistical methods to study patterns and trends in populations.