1. Department of Epidemiology and Biostatistics Indiana University Bloomington School of Public Health Bloomington IN USA
2. MRC/Wits Rural Public Health and Health Transitions Research Unit, School of Public Health University of the Witwatersrand Johannesburg, South Africa Faculty of Health Sciences Johannesburg South Africa
3. Division of Endocrinology, Diabetes and Metabolism Perelman School of Medicine, University of Pennsylvania Philadelphia PA USA
4. Department of Chemical Pathology National Health Laboratory Service, University of the Witwatersrand Johannesburg Faculty of Health Sciences Johannesburg South Africa