The CHA2DS2-VASc score has been evaluated in at least ve separate cohorts since its original description. With the exception of a recent study by Olesen et al,24 all other studies have found that the predictive ability of CHA2DS2-VASc is similar to that of the CHADS2 score (C statistics of each risk score is 0.6 across the various studies) and not statistically signi cantly greater than that of CHADS2.36,40-43 Because the CHADS2 score has been extensively validated and is easy for clinicians to remember and use, we use the CHADS2 score as the principal approach for our risk-based treatment recommendations. 1.4.4 Estimating the Baseline Risk of Nonfatal Stroke by CHADS2 Score: To develop our recommendations, we required estimates of the absolute rate of nonfatal stroke (ischemic or hem- orrhagic) for patients according to their underlying risk of stroke, as characterized by their CHADS2 score. Ideally, we would obtain these estimates of baseline risk from published annual rates of stroke, by CHADS2 score, among untreated patients. However, such data are not available. Therefore, to obtain estimates of annual stroke risk, we used pooled data from aspirin-treated patients enrolled in six clinical trials of antithrombotic therapy for stroke prevention in AF.37 This published report presented data regarding ischemic stroke rates (fatal and nonfatal combined) on aspirin, strati ed by CHADS2 score. We used the following calculations to estimate the annual risk of nonfatal stroke (ie, ischemic and hemorrhagic) on aspirin: (1) multiplication of reported rates of ischemic stroke by 1.08 to account for additional hemorrhagic strokes on aspirin therapy (based on the observed ratio of ischemic:hemorrhagic strokes in aspirin arms of RCTs in patients with AF) and (2) an estimation that 50% and 25% of hemorrhagic and ischemic strokes, respec- tively, were fatal. 