Key points are not available for this paper at this time.
From the Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford, England. *A similar essay originally appeared in the British Medical Journal and has reappeared at the invitation of several other journals. Address for correspondence: David Sackett, MD, Center for Evidence-Based Medicine, John Radcliffe Hospital, Oxford, OX3 9DU England.
David L. Sackett (Fri,) studied this question.