1. Radboud University Nijmegen Medical Center; Institute for Quality of Health Care (IQ health care); PO Box 9101 Nijmegen Netherlands 6500 HB
2. Maastricht University; Department of Epidemiology; P.O. Box 616 Maastricht Netherlands 6200 MD
3. VU University Medical Center; Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research; PO Box 7057 Amsterdam Netherlands 1007 MB
4. University Medicine Goettingen; Nikolausberger Weg 126 Goettingen Germany D-37075
5. University of Maastricht; Epidemiology; Debyeplein 1 Maastricht Netherlands 6200 MD