Ritchwood TD, Hughes JP, Jennings L, MacPhail C, Williamson B, Selin A, Kahn K, Gómez-Olivé FX, Pettifor A. Characteristics of Age-Discordant Partnerships Associated With HIV Risk Among Young South African Women (HPTN 068). J Acquir Immune Defic Syndr. 2016 Aug 01; 72(4):423-9.