- Correspondence to Peter F Kemper, Department of Public and Occupational Health, EMGO+ Institute for Health Care and Research, VU University Medical Center, Van der Boechorststraat 7, Amsterdam 1081 BT, The Netherlands;
- Received August 15, 2012
- Revised December 28, 2012
- Accepted January 16, 2013
- First published February 14, 2013.
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