1. Department of Clinical Epidemiology; Leiden University Medical Center; Leiden the Netherlands
2. Department of Clinical Pharmacy and Toxicology; Leiden University Medical Center; Leiden the Netherlands
3. Department of Thrombosis and Hemostasis; Leiden University Medical Center; Leiden the Netherlands
4. Anticoagulation Clinic The Hague; The Hague the Netherlands
5. Anticoagulation Clinic Utrecht; Utrecht the Netherlands