- Correspondence to Professor Daniel Kotz, Addiction Research and Clinical Epidemiology Unit, Medical Faculty of the Heinrich-Heine, University Düsseldorf, Institute of General Practice, Düsseldorf 40225, Germany;
- Received 26 January 2017
- Revised 17 March 2017
- Accepted 4 April 2017
- Published online 4 May 2017.
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