1 Center for Clinical Transfusion Research, Sanquin Research, Leiden, The Netherlands and Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands R.A.Middelburg@lumc.nl.
2 Center for Clinical Transfusion Research, Sanquin Research, Leiden, The Netherlands and Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands.
3 Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands.