New research shows how Londoners used death data to survive the plague

New research by the University of Portsmouth reveals that during the Great Plague of 1665, Londoners used published death figures to make daily, life or death decisions, reshaping how governments managed public health and personal freedom for the first time. 

Drawing on the famous diary of Samuel Pepys, the study shows how weekly death reports known as the ‘Bills of Mortality’ acted as an early form of public health data. Far from being dry statistics, these figures influenced where people went, who they met, and whether they stayed in the city or fled. They also helped justify unprecedented government actions, including quarantine, travel restrictions and the suspension of everyday liberties. 

The research offers a rare, ground-level view of how people lived through a public health emergency centuries before modern medicine - highlighting striking parallels with how data is used today during health outbreaks. 

“Pepys wasn’t just recording history, he was using death figures to decide how to live,” said Professor Karen McBride, School of Accounting, Economics and Finance at the University of Portsmouth. “His diary shows us, week by week, how published death numbers shaped fear, behaviour and trust in government. It’s one of the earliest examples of data being used to manage both populations and personal risk.” 

While the ‘Bills of Mortality’ helped people assess danger, the study also reveals how their impact was deeply unequal. Wealthier Londoners, including Pepys, could read the figures and leave the city, while poorer residents - living in overcrowded conditions and with less access to information - were more likely to be exposed, restricted and left behind. 

The findings challenge the idea that data-driven public health is a modern invention. Instead, they show how counting deaths became a powerful political and social tool, one that expanded government authority while quietly shifting responsibility onto individuals to manage their own safety. 

“This research reminds us that debates surrounding accounts and accountability, trust and public freedom are not new,” added Professor McBride. “They were already playing out on the streets of 17th-century London.” 

The study highlights the origins of public health policy, surveillance and statistical thinking and questions how societies balance protection, power and personal freedom in times of crisis.