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Figure 4 Analysis of thromboembolic risk in three studies of patients with lone atrial fibrillation according to the number of risk factors for stroke and age. (From Gersh BJ, Antithrombotic therapy in nonrheumatic/nonvalvular atrial fibrillation. J Cardiovasc Electrophysiol 1999;10:461–71. By permission of Futura Publishing Company).