Epidemiology is a basic medical science that is fundamental to understanding diagnosis, treatment, and prognosis.Diagnosis requires answers to a series of questions: is this patient sick or well? If sick, what are the chances of a particular disease causing the problem? What investigations will be most useful in obtaining the diagnosis? Epidemiology applied to the bedside problems of patients - clinical epidemiology - can help to provide solutions. The ability of a detail of the patient's history, or a clinical sign which could confirm or disprove diagnosis can be described by using simple arithmetic. The probability that a disease is or is not present can be given a numerical value, and the extent to which investigation increases or reduces the likelihood of discovering disease can also be measured.Stroke is one of the most common diagnoses made by physicians. Patients with signs and symptoms suggestive of stroke require careful assessment to avoid diagnostic error.This book is written by a clinician who is also trained in epidemiology and is intended for clinicians who treat patients with stroke, for epidemiologists who want to apply epidemiology to clinical problems, for therapists who wish to develop their understanding of the application of scientific method to rehabilitation practice, and for medical students who may wish to accelerate and complement the process of acquiring clinical experience about stroke.