- Correspondence to Dr Tingting Yao, Institute for Health & Aging, School of Nursing, University of California, San Francisco, 3333 California Street, Suite 340, San Francisco, CA 94118, USA;
- Received September 9, 2016
- Revised March 29, 2017
- Accepted May 8, 2017
- First published July 26, 2017.
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