 Analysis of the Bills of Mortality during the months plague took hold shows a rise in deaths other than by plague well above the average death rate, which has been attributed to misrepresentation of the true cause of death.As plague spread, a system of quarantine was introduced, whereby any house where someone had died from plague would be locked up and no one allowed to enter or leave for 40 days.This frequently led to the deaths of the other inhabitants, by neglect if not from the plague, and provided ample incentive not to report the disease.