1. School of Public Health, Peking University; Centre for Evidence Based Medicine and Clinical Research, Department of Epidemiology and Biostatistics; 38 Xueyuan Road, Haidian District Beijing China 100191
2. Shantou University Medical College; Shantou-Oxford Clinical Research Unit; Shantou, Guangdong China 515041
3. McMaster University; Department of Clinical Epidemiology and Biostatistics; 1280 Main Street West Hamilton Ontario Canada L8S4K1
4. Peking University People's Hospital; Department of Endocrinology; 11 Xizhimen South Street Xicheng District Beijing China 100044
5. Peking University Third Hospital; Department of Endocrinology; 49 North Huayuan Road Haidian District Beijing China 100191