Users' guides to the medical literature. VII. How to use a clinical decision analysis. A. Are the results of the study valid? Evidence-Based Medicine Working Group

CLINICAL SCENARIO You are the attending physician on an inpatient service where a 51-year-old man is admitted with congestive heart failure of recent onset. You find he has a dilated cardiomyopathy, the cause of which remains unknown after a thorough evaluation. He is in sinus rhythm. The team's resident asks you whether the patient should be anticoagulated with warfarin, enough to keep his international normalized ratio from 2.0 to 3.0, in order to prevent systemic emboli, even though his echocardiogram does not show left ventricular thrombus. You are not sure about the evidence concerning this issue, so you admit your shared knowledge gap and resolve to search together for the relevant information. THE SEARCH In the hospital's library, the two of you search the MEDLINE system us