1 Cecil G. Sheps Center for Health Services Research and Departments of Family Medicine and Internal Medicine, School of Medicine, University of North Carolina, Chapel Hill, NC, USA. Electronic address: [email protected].
2 Departments of Medicine and Ophthalmology, Duke University School of Medicine, Durham, NC, USA.
3 Division of Speech and Hearing Sciences, Department of Allied Health Sciences, School of Medicine, University of North Carolina, Chapel Hill, NC, USA.