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 With VKA With ASA With VKA CI) 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 . aspirin Warfarin: daily medication, lifestyle limitations, dietary restrictions, frequent blood testing and clinic visits High Aspirin: daily medication only ASA acetylsalicyclic acid; BAFTA Birmingham Atrial Fibrillation of the Aged; NASPEAF National Study for Prevention of Embolism in Atrial Fibrillation; PATAF Primary Prevention of Arterial Thromboembolism in Nonrheumatic AF in Primary Care Trial; SIFA Studio Italiano Fibrillazione Artiale; WASPO Warfarin vs Aspirin for Stroke Prevention in Octogenarians With AF. See Table legends for expansion of other abbreviations. a Pooled estimates of treatment effect in this evidence pro le are from a new meta-analysis of data from RCTs which included a comparison of warfarin and antiplatelet monotherapy (typically aspirin). In SPAF III and AFASAK II, aspirin was combined with xed (ineffective) minidose warfarin (AFASAK I, AFASAK II, Vemmos et al , BAFTA, EAFT, NASPEAF, PATAF, SIFA, SPAF II, SPAF III, WASPO). b The CI does not exclude the possibility of 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) and an estimated relative risk of mortality of for aspirin vs no therapy ( Table ). d Intracranial hemorrhage includes intracerebral, subdural, and subarachnoid bleeds. 