T. Gill 1 , C. Williams 1 ; 1 Yale University School of Medicine, New Haven, CT PURPOSE: When determining the incidence of disability, long assessment intervals maybe problematic because they do not account for the possibility of recovery not for losses to followup due to deaths. In this study, we tested two related hypotheses: (1) longitudinal studies with long assessment intervals underestimate the incidence of disability; and (2) these underestimates increase as the length of the assessment interval increases.