1. Department of Community and Family Medicine, Psychiatry and Behavioral Science, and Psychology and Neuroscience, Duke University Medical Center, Durham, NC.
2. Department of Community and Family Medicine, Duke University Medical Center, Durham, NC.
3. Department of Statistical Science, Duke University, Durham, NC.
4. Department of Biological Sciences, North Carolina State University, Raleigh, NC.
5. Department of Obstetrics and Gynecology, Duke University Medical Center, Durham, NC.