 In order to judge the severity of an epidemic, it is first necessary to know how big the population was in which it occurred.There was no official census of the population to provide this figure, and the best contemporary count comes from the work of John Graunt (1620–1674), who was one of the earliest Fellows of the Royal Society and one of the first demographers, bringing a scientific approach to the collection of statistics.In 1662, he estimated that 384,000 people lived in the City of London, the Liberties, Westminster and the out-parishes, based on figures in the Bills of Mortality published each week in the capital.