Brian S. Everitt - Professor Emeritus, King's College London. After 35 Years at the Institute of Psychiatry, University of London, Brian Everitt retired in May 2004. Author of approximately 100 journal articles and over 50 books on statistics, and also -co-editor of Statistical Methods in Medical Research. Writing continues apace in retirement but now punctuated by tennis, walks in the country, guitar playing and visits to the gym, rather than by committees, committees and more committees. Christopher R. Palmer, founding Director of Cambridge University's Centre for Applied Medical Statistics, regularly teaches and collaborates with current and future doctors. His first degree was from Oxford, while graduate and post-doctoral studies were in the USA (at UNC-Chapel Hill and Harvard). He has shifted from mathematical towards applied statistics, with particular interest in the ethics of clinical trials and the use of flexible designs whenever appropriate. Fundamentally, he likes to promote sound statistical thinking in all areas of medical research and hopes this volume might help towards that end. Chris served as Deputy or Acting Editor of Statistics in Medicine, 1996-2000, and is a long-standing statistical reviewer for The Lancet. he and his wife have three children they consider to be more than Statistically significant.