After 13 years there are new areas to discuss and more recent trials to be included. Good clinical practice; evaluation of quality of life; measurement of the benefit: risk comparison; determination of cost- effectiveness and cost utility; stopping rules for trials; meta-analysis and subgroup analysis are all new sections. The references are expanded from 305 to 512 and include the recent advances in trial design, such as the n-of-1 trials and megatrials, and up-to-date examples to illustrate the points made in the 20 chapters.