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in addition to the points raised by dr ghosh's correspondent, you might want to consider that specificity should fall as you move from primary to tertiary care for any clinical finding or test that serves as a stimulus for referral. ameen patel reported that a few year's ago (Patel A, Sackett DL. The Referral Forces that Raise Prevalence Also Lower Specificity. Clinical Research, Vol 40, No 2, 1991, 370A.) but it's even more complex than that, as jim wagner is showing in the study he's leading into the diagnosis of appendicitis. if primary care folks over-read a sign (raising its sensitivity so that they don't miss any true positives) specificity may rise in tertiary care. a couple of morals to this tale: 1. us secondary and tertiary clinicians need to be more careful about what we teach GP-trainees about the usefulness of signs and symptoms. 2. we might want to lighten up on our criticism of our tertiary care colleagues for jumping to imaging or other high-tech investigations early in their evaluations of patients: to the extent that we do proper histories and physical exams before we refer patients, the diagnostic power of the signs and symptoms will be "used up" before they get to the sub-specialists. cheers dls ............................................................................ Prof David L. Sackett Director, NHS R&D Centre for Evidence-Based Medicine Consultant in Medicine Editor, Evidence-Based Medicine Nuffield Department of Medicine, University of Oxford Level 5, John Radcliffe Hospital, Oxford OX3 9DU, England Phone: +44-(0)1865-221320 Fax: +44-(0)1865 222901 Email: [log in to unmask] WWW: http://cebm.jr2.ox.ac.uk ............................................................................ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%