- Correspondence to Maria Christine Magnus, Norwegian Institute of Public Health, Division of Epidemiology, Department of Chronic Diseases, PO Box 4404, Nydalen, N-0403 Oslo, Norway;
- Received 13 October 2014
- Revised 5 December 2014
- Accepted 12 December 2014
- Published in print 1 March 2015.
- Published online 16 February 2015.
- Published first 8 January 2015.
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