Review articles synthesize in narrative form the best available evidence on a topic. Review articles are only
published as part of Supplements to PLOS Medicine and are not featured in the PLOS Medicine Magazine.
South African Department of Science and Technology/National Research Foundation Centre for Excellence in Epidemiological Modelling and Analysis, University of Stellenbosch, Stellenbosch, South Africa,
International Centre for Reproductive Health, Ghent University, Ghent, Belgium