- Correspondence to Mark Goodchild, World Health Organization, 20 avenue Appia, 1211 Geneva 27, Switzerland;
- Received 10 July 2016
- Revised 26 October 2016
- Accepted 18 November 2016
- Published in print 4 January 2017.
- Published online 2 February 2017.
- Published first 30 January 2017.
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