- Correspondence to Marieke R Potijk, Department of Health Sciences, Community and Occupational Medicine, University Medical Center Groningen, University of Groningen, Antonius Deusinglaan 1, PO Box 196, 9700 AD Groningen, The Netherlands;
- Received April 1, 2011
- Accepted October 21, 2011
- First published December 6, 2011.
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