of Studies Risk of Bias Inconsistency Indirectness Imprecision Publication Bias Study Event Rates (%) Relative Effect CI) Estimation of Absolute Effects y Time Frame Quality of Evidence With No Therapy With Antiplatelet With No Therapy With Antiplatelet CI) Systemic embolism (important outcome) mean follow-up y RCTs No serious limitations No serious inconsistency No serious indirectness Imprecise l Undetected RR per m fewer systemic embolism per (from fewer to more) Moderate ESPS European Stroke Prevention Study; JAST Japan Atrial Fibrillation Stroke Trial; LASAF Low-dose Aspirin, Stroke, Atrial Fibrillation; SAFT Swedish Atrial Fibrillation Trial; UK-TIA United Kingdom Transient Ischaemic Attack Aspirin Trial. See Table legends for expansion of other abbreviations. a Pooled estimates of treatment effect in this evidence pro le, with the exception of nonfatal major extracranial bleeding b , are from a meta-analysis conducted for these guidelines, including data from RCTs of antiplatelet monotherapy (typically aspirin) vs no therapy (AFASAK I, SPAF I, EAFT, UK-TIA, LASAF, JAST, SAFT). b To obtain a best estimate of the risk of nonfatal major extracranial bleeding on antiplatelet monotherapy, we used data from the Antithrombotic Trialists Collaboration meta-analysis of aspirin for the secondary prevention of cardiovascular disease. c The CI does not exclude the possibility of no effect. d From Go et al, which reported a mortality rate of per person-y in untreated (no warfarin) patients from an observational study (ATRIA cohort). e Intracranial hemorrhage includes intracerebral, subdural, and subarachnoid bleeds. For studies that did not report the number of strokes that were fatal and nonfatal (EAFT, UK-TIA, JAST), we imputed values for the number of fatal and nonfatal strokes to estimate the pooled relative risk for nonfatal stroke across all eligible studies. Assumptions underlying these estimates are detailed in section of this article. 