- Correspondence to Professor Jing Liu, Department of Epidemiology, Beijing Anzhen Hospital, Capital Medical University, Beijing Institute of Heart, Lung and Blood Vessel Diseases, No. 2 Anzhen Street, Chaoyang District, Beijing, China;
- Received May 6, 2014
- Revised September 16, 2014
- Accepted October 3, 2014
- First published October 23, 2014.
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