Thomas Nettleton and the dawn of quantitative assessments of the effects of medical interventions.

Thomas Nettleton (1683–1742) was one of the first, possibly the first, to use quantitative assessments of the effects of medical interventions. Prior to establishing a medical practice in Halifax, West Yorkshire, Nettleton had been educated at Bradford Grammar School, and had studied medicine at Edinburgh and Leyden, where he was awarded his Doctorate of Medicine. In December 1721, during an epidemic of smallpox in West Yorkshire and frustrated by the lack of any effective therapy for the disease, Nettleton began to use variolation, which at the time was known as inoculation. Variolation to immunize people against smallpox was introduced into Europe and North America in 1721. However, there was uncertainty and debate about whether it did more good than harm. To address this uncertainty, Nettleton collected statistics on the mortality associated with naturally-acquired smallpox and compared these with mortality following variolation. He communicated his findings in a series of letters and a pamphlet published in 1722 and 1723.