1 Department of Philosophy, University of Johannesburg, Jonannesburg, South Africa.
2 Leiden University Medical Center, Department of Clinical Epidemiology, Leiden, The Netherlands and Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
3 Department of Medical Statistics and Centre for Global NCDs, London School of Hygiene and Tropical Medicine, London, UK and Centre for Public Health Research, Massey University, Wellington, New Zealand.