Busy doctors have never had time to read all the journals in their disciplines. There are, for example, about 20 clinical journals in adult internal medicine that report studies of direct importance to clinical practice, and in 1992 these journals included over 6000 articles with abstracts: to keep up the dedicated doctor would need to read about 17 articles a day every day of the year.1 In earlier eras limitations in our understanding of human biology and the absence of powerful clinical research methods meant that major advances were published far less commonly than now. Consequently, clinicians' failure to keep up did not harm patients. Not any more. Rapid advances in physics, chemistry, and molecular biology since the second world war have led to a huge increase in the possibilities for managing patients. Effective treatments have appeared often for the first time. In parallel with these scientific advances researchers have developed methods of applied research—epitomised by the randomised controlled trial—to identify which new ideas for diagnosis, treatment, and predicting outcome actually work. Many do not and may do more harm than good. Doctors need to …