- Correspondence to Dr Tianjing Li, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, E6011 Baltimore, MD 21205, USA;
- Received 22 September 2016
- Revised 5 January 2017
- Accepted 12 February 2017
- Published in print 1 October 2017.
- Published online 26 September 2017.
- Published first 7 March 2017.
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