1. Erasmus Medical Center; Department of General Practice; PO Box 2040 Rotterdam Netherlands 3000 CA
2. Vjverberg 37 Den Bosch Netherlands 5223 ZP
3. Erasmus Medical Center; PO Box 2040 Rotterdam Netherlands 3000 CA
4. Maastricht University; Department of Epidemiology; P.O. Box 616 Maastricht Netherlands 6200 MD