Letter by Nielsen and Søgaard Regarding Article, “Rivaroxaban Versus Apixaban for Stroke Prevention in Atrial Fibrillation: An Instrumental Variable Analysis of a Nationwide Cohort”

Aalborg Thrombosis Research Unit, Department of Clinical Medicine, Faculty of Health, Aalborg University, Denmark (P.B.N., M.S.).

Department of Cardiology, Aalborg University Hospital, Denmark (P.B.N., M.S.).