1. Department of Hematology, Erasmus University Medical Center, 's-Gravendijkwal 230, 3015 CE Rotterdam, The Netherlands
2. Star-Medical Anticoagulation Clinic, Vlambloem 21, 3068 JE Rotterdam, The Netherlands
3. Department of Thrombosis and Haemostasis, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands
4. Department of Clinical Epidemiology, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands