1. a Center for Pharmaceutical Marketing and Management , University of Mississippi , Oxford , MS , USA
2. b Department of Health Behavior and Health Education, School of Public Health , University of North Carolina , Chapel Hill , NC , USA
3. c Division of General Medicine and Clinical Epidemiology, School of Medicine , University of North Carolina , Chapel Hill , NC , USA
4. d Cecil G. Sheps Center for Health Services Research , University of North Carolina , Chapel Hill , NC , USA
5. e Center for AIDS Research , University of North Carolina , Chapel Hill , NC , USA
6. f Division of Infectious Diseases, School of Medicine , University of North Carolina , Chapel Hill , NC , USA
7. g Department of Biostatistics, School of Public Health , University of North Carolina , Chapel Hill , NC , USA