- Correspondence to Karin Veldman, Department of Health Sciences, Community & Occupational Medicine, University Medical Center Groningen, P.O. Box 196, FA 10, Groningen 9700 AD, The Netherlands;
- Received May 21, 2014
- Revised November 10, 2014
- Accepted January 14, 2015
- First published February 9, 2015.
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