“…Common administrative retention strategies were to obtain multiple alternate contact numbers for participants [37,53,64], make multiple (10-20) contacts with participants during the study period [31,38,39,45,53,54,57], and maintain detailed databases and tracking registries for participants [29,37,59]. Providing financial or other incentives, transportation, or childcare were also commonly mentioned [29, 37-40, 42, 43, 45, 46, 48-50, 54-59, 63, 64].…”