Professor Peter Sandercock, Personal Chair in Medical Neurology, presents the fourth lecture in the 2014 Medical Detectives series entitled, Unravelling the Mystery of Stroke Disease - The Clue's in the Numbers... Ideas about the causes of stroke have evolved over the centuries from the mystical to the realisation that most strokes are due to a plumbing problem - a blocked or burst artery in the brain. In this lecture Professor Peter Sandercock will begin by describing early attempts to map stroke in the population and then explain how the numerical science of epidemics of infectious diseases in populations was successfully applied to stroke to identify its main causes. Recorded on 6 November 2014 at the University of Edinburgh's Anatomy Lecture Theatre.