Epidemiology: A Very Short Introduction explains what epidemiology is and its importance to the discovery, control, and prevention of disease in world populations. It looks at health hazards identified by the study of epidemiology — such as the relationship between tobacco smoking and lung cancer and between various aspects of diet, environment, and exercise — and the origin and spread of new epidemics. This VSI dispels some of the myths surrounding the study of epidemiology. It explores the principles behind clinical trials and explains the nature of the basic statistics concerning disease. It also considers the ethical and political issues related to obtaining and using information concerning patients and trials involving placebos.