1. Cardiff Univeristy; Cardiff School of Biosciences; PO Box 915 Cardiff UK CF10 3TL
2. Amsterdam UMC Vrije Universiteit; Department of General Practice and Elderly Care Medicine, Amsterdam Public Health Research Institute; PO Box 7057 Amsterdam Netherlands 1007 MB
3. Erasmus Medical Center; Department of General Practice; PO Box 2040 Rotterdam Netherlands 3000 CA