1 Evidence-Based Medicine Center of Lanzhou University, Lanzhou, Gansu, China.
2 Department of Epidemiology and Health Statistics, West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, Sichuan, China.
3 Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, ON L8S 4L8, Canada. Electronic address: yaol12@mcmaster.ca.