1. Division of Epidemiology & Biostatistics, Department of Global Health, Faculty of Health Medicine & Health Sciences, Stellenbosch University, Cape Town, South Africa
2. Division of Epidemiology & Biostatistics, School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
3. University of North Carolina at Chapel Hill, NC, USA
4. Northumbria University, Department of Mathematics, Physics and Electrical Engineering, Faculty of Engineering and Environment, Newcastle upon Tyne, UK