1. The Ohio State University; Division of Epidemiology; Columbus Ohio USA
2. University of North Carolina; Dept. of Obstetrics and Gynecology; Chapel Hill North Carolina USA
3. FHI 360; Clinical and Epidemiological Sciences; 359 Blackwell St, Suite 200 Durham North Carolina USA 27701
4. FHI 360 and UNC School of Medicine; Quantitative Sciences; 359 Blackwell Street, Suite 200 Suite 200 Durham North Carolina USA 27701