Statistics is a subject which generally induces mental paralysis, occasionally contempt and, at the very least apathy in its users. Nevertheless, statistics have been a great aid to and are an integral part of scientific advancement and their importance cannot be denied. Even though this is recognized by the medical student, the practising physician and the research worker, medical statistics is still to many a dark territory which should not be invaded. The problem then, is to impart a knowledge of statistics to learners in a manner which inflicts the minimum of pain, but at the same time equips them with sufficient understanding to enable them to tackle their statistical problems cautiously, logically and correctly. This book is directed explicitly towards the medical applications of statistics in that some of the statistical methodology described and most of the examples included are peculiar to the medical field. The topics covered are those which constitute an elementary course in statistics and the book is intended to serve as a useful adjunct to lectures and fuller texts, providing the student with an outline for revision and the medical research worker with an instructive handbook. The structure and format of this new second edition remain basically the same as those of the first, although as a result of popular demand or as a consequence of the development of statistical theory from the publication of the first edition in 1978, the entire text has been revised.