1 Department of Epidemiology and Department of Global Health, Boston University School of Public Health, Boston, MA 02476, USA; Health Economics and Epidemiology Research Office, Department of Internal Medicine, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. Electronic address: mfox@bu.edu.
2 Department of Epidemiology, Biostatistics, & Occupational Health, McGill University, Montreal, QC, Canada.