Cohort and other studies with longitudinal designs often struggle to maintain their recruited participants across all the study time points and to obtain complete data. The problems reduce the effective sample size quality of the evidence and robustness of the findings, and can undermine the often substantial investment in such studies. Researchers are devoting increasing amounts of time and resources to understand how participants decide to take part in research and what researchers can do to make their work appeal to potential participants. We will explore some of these issues within NICOLA and, to our knowledge, no similar work has been conducted solely within an over 50 population.