The overall goal is to improve outcomes among patients with atrial fibrillation (AF) by preventing stroke. The investigators propose to implement an automated algorithm using electronic medical record (EMR) data to alert physicians in a large primary care practice network at the Massachusetts General Hospital (MGH) of their patients with AF and elevated stroke risk that are not taking an anticoagulant for stroke prevention. The investigators hypothesize that interventions to notify physicians of such individuals may prompt reassessment for the need for anticoagulation, and thereby increase guideline-indicated anticoagulation rates. Additionally, in a survey component, physicians will characterize reasons for not pursuing anticoagulation in AF patients at elevated risk for stroke.