This book is primarily aimed at medical researchers and may also be useful to medical students, to clinicians who wish to understand the principles of the design and analysis of research, and to those attending postgraduate courses in medical statistics. The book aims to provide an understanding of the basic principles that underlie research design, data analysis and the interpretation of results and to enable the reader to carry out a wide range of statistical analyses. The emphasis is on the practical aspects of the design and analysis of medical research and attention is paid to the interpretation and presentation of results. By discussing the use and misuse of statistics the book aims to give the reader the material to judge the appropriateness of the methods and interpretation in papers published in medical journals. In most of the cases contained in the book the raw data is given so that analyses can be reproduced either by computer or by hand calculation.