- Correspondence to Professor Thomas Behrens, Institute for Prevention and Occupational Medicine of the German Social Accident Insurance (IPA) Institute of the Ruhr-Universität Bochum, Bürkle-de-la-Camp-Platz 1, Bochum 44789, Germany;
- Received February 21, 2013
- Revised June 18, 2013
- Accepted July 11, 2013
- First published August 2, 2013.
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