1. Department of Health and Experimental Sciences; Unit of Research in Occupational Health; Pompeu Fabra University Dr Aiguader, 80 Barcelona Spain 08003
2. Hospital de la Santa Creu i Sant Pau; Spanish Cochrane Centre, Department of Epidemiology; c/ Sant Antoni M. Claret, 167 Barcelona Catalonia Spain 08025
3. Center for Health Services Research; 1 Ford Place Suite 3A Detroit USA MI 48202-3450
4. Health Department; Subdireccio General de Salut Publica; Roc Boronat 81-95 08005 Barcelona Catalonia Spain