of Studies Risk of Bias Inconsistency Indirectness Imprecision Publication Bias Study Event Rates (%) Relative Effect CI) Estimation of Absolute Effects Time Frame Quality of Evidence With ASA Clopid With VKA With ASA Clopid With VKA CI) Systemic embolism (important outcome) median follow-up y RCT No serious limitations a No serious inconsistency No serious indirectness No serious imprecision Undetected RR per k fewer systemic emboli per (from fewer to fewer) High Burden of treatment (important outcome) N/A No serious limitations No serious limitations No serious limitations No serious limitations N/A N/A N/A VKA . ASA clopidogrel Warfarin: daily medication, lifestyle limitations, dietary restrictions, frequent blood testing and clinic visits High Aspirin clopidogrel: daily medication only ACTIVE Atrial Fibrillation Clopidogrel Trial With Irbesartan for Prevention of Vascular Events. Clopid clopidogrel. See Table and legends for expansion of other abbreviations. a Results are based on a single RCT (ACTIVE W) that was stopped early for bene t. b The CI does not exclude appreciable harm or bene t with VKA therapy. c Based on data from Go et al, which reported a mortality rate of per person-y in untreated (no warfarin) patients from an observational study (ATRIA cohort), an estimated relative risk of for mortality with aspirin vs no therapy ( Table ), and an estimated relative risk of for mortality with aspirin clopidogrel vs aspirin ( Table ). d Intracranial hemorrhage includes intracerebral, subdural, and subarachnoid bleeds. The published report did not provide the number of strokes that were fatal and nonfatal; therefore, we imputed values for the number of fatal and nonfatal strokes to estimate the relative risk for nonfatal stroke. Assumptions underlying these estimates are detailed in section of this article. e Of the nonfatal strokes on aspirin clopidogrel therapy, an estimated were ischemic, and ve were hemorrhagic. 