- Correspondence to Hongzhuan Tan, Department of Epidemiology and Health Statistics, School of Public Health, Central South University, No 88 Xiangya Road, Changsha, Hunan 410008, the People's Republic of China;
- Received February 8, 2012
- Revised July 18, 2012
- Accepted July 28, 2012
- First published September 1, 2012.
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