The purpose of this study is to investigate the efficacy and safety of non-vitamin K antagonist oral anticoagulants (NOAC) in atrial fibrillation patients with intermediate stroke risk (CHA2DS2-VASc score 1 for male, 2 for female). A. Major safety results include major bleeding and clinically relevant non-major bleeding. B. Major efficacy results include strokes, systemic embolism and cardiovascular mortality. C. Other results include myocardial infarction, pulmonary embolism, transient ischemic attack, hospitalization, drug compliance, quality of life questionnaire (AFEQT), cognitive function (KDSQ), aging questionnaire(K-Frail) and hand grip strength.