Page:William Petty - Economic Writings (1899) vol 1.djvu/99

Rh when a sufficient series of years is taken, the discrepancy arising from this source during the seventeenth century is not large. And, finally, the number of persons who died in London but were buried in the country far exceeded the number dying in the country but buried in London. How great the error due to this fact may have been in the seventeenth century, we have no means of knowing. In the middle of the eighteenth it was very plausibly calculated at one sixth of the whole number. Taking all these facts into account, it is not too much to assume that we must add a correction of at least fifteen per cent. to the figures of burials in the pre-Restoration bills, and not less than ten per cent. to the later figures which Petty uses, in order to obtain an approximately correct estimate of the actual mortality of London at the dates in question. Inasmuch as both Graunt and Petty base their estimates of London's population upon the burials reported in the bills, the numbers which they deduce must be pronounced too small, even upon the assumption of a death rate that justified them in multiplying by only thirty. But their other important deductions from the bills, such as the determination of the approximate numerical equality between the sexes, the discovery that the most healthy years are also the most fruitful, and even their calculations of the growth of the city, are far less affected by the incompleteness of the original returns. In fact if the cases omitted were, as seems not improbable, similar or proportional to those included, the effect of the omissions upon the validity of most of their conclusions would be almost negligibly small.

So far as the "country bills" used by Graunt are concerned, it is probable that the parish registers from which they were derived were kept more carefully after Cromwell's registration Act of 1653 than before it. If so we can account not only for the increase of the weddings, which Graunt explains in another way, but also for the contemporaneous increase of the births and the burials.