1. School of Mathematics, Department of Statistical Science, Sun Yat-Sen University, Guangzhou, China;
2. School of Mathematics, Department of Statistical Science, Southern China Center for Statistical Science, Sun Yat-Sen University, Guangzhou, China;
3. Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China;
4. Xinhua College, Sun Yat-Sen University, Guangzhou, 510520, China;
5. School of Public Health, Yale University, New Haven, CT;
6. University of Texas MD Anderson Cancer Center, Houston, TX