1 Department of Psychology and Psychotherapy, University of Witten/Herdecke, 58448 Witten, Germany. Electronic address: thomas.ostermann@uni-wh.de.
2 University of Applied Sciences, 2333 CK Leiden, Netherlands; Department of Healthcare and Nutrition, Louis Bolk Institute, 3972 LA Driebergen, Netherlands.
3 Personal Social Services Research Unit, London School of Economics and Political Science, London WC2A 2AE, UK. Electronic address: D.Mcdaid@lse.ac.uk.