Retaining and tracking cohort study members.

The only way to ensure that losses to follow-up have not biased study results is to keep all losses to an absolute minimum. Since more complete follow-up leads to the identification of additional disease events, the effort spent in locating cohort members also improves the precision as well as the validity of the study results. This presentation reviewed approaches for maximizing retention and minimizing loss to follow-up, including the importance of communicating the expectations of participation and collecting personal information at baseline, conducting frequent personal and mail contact, and providing incentives for participation. Response rates can be increased by repeated attempts to contact each cohort member using a range of approaches (e.g., telephone, mail, personal contacts) and by other procedures specific to mailed questionnaires, telephone interviews, or in-person visits. Lost participants can be traced by use of the NCOA system and contact with other local, state, and national sources. Finally, for those participants who are unable or unwilling to continue or who cannot be found, proxy interviews and/or use of the National Death Index may provide information on the outcomes of interest and vital status. Additional research evaluating the efficacy of the various approaches to retention and tracking is needed to help investigators learn how to best apply study resources to retain and keep track of the largest possible number of cohort members.