1. Department of Clinical Epidemiology, Leiden University Medical Center, Albinusdreef 2, Box 9600, Leiden 2300 RC, The Netherlands
2. Department of Haematology, University Medical Center Groningen, University of Groningen, Hanzeplein 1, Groningen 9713 GZ, The Netherlands
3. Department of Internal Medicine, Section of Thrombosis and Haemostasis, Leiden University Medical Center, Albinusdreef 2, Box 9600, Leiden 2300 RC, The Netherlands