- Correspondence to Dr Zhaoli Dai, Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, 650 Albany St, Boston, MA 02118, USA;
- Received 11 November 2016
- Revised 8 February 2017
- Accepted 20 March 2017
- Published in print 4 May 2017.
- Published online 23 May 2017.
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