1. Institute of Medical Sciences, University of Toronto, Toronto, Ontario, Canada
2. Department of Biostatistics, Brown University, Providence, Rhode Island
3. Division of Epidemiology and Biostatistics, Mel and Enid Zuckerman College of Public Health, University of Arizona, Tucson
4. Department of Behavioral Sciences, College of Health Sciences, Moi University, Eldoret, Kenya
5. Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada6Department of Medicine, College of Health Sciences, School of Medicine, Moi University, Eldoret, Kenya7Department of Epidemiology, Fairbanks Scho