1. Department of Social Medicine, Faculty of Medicine, Vrije Universiteit Amsterdam, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
2. Institute for Research in Extramural Medicine, Faculty of Medicine, Vrije Universiteit Amsterdam, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
3. TNO Work and Employment, P.O. Box 718, 2130 AS, Hoofddorp, The Netherlands