Understanding loss to follow-up in a longitudinal study of people with traumatic brain injury.

To examine factors related to attrition in a traumatic brain injury (TBI) study sample assessed up to 15 years after injury.
One thousand twenty-eight participants with TBI who completed the year 1 follow-up assessment at a TBI Model Systems Center between 1992 and 2018.
Secondary analysis of data from a prospective longitudinal cohort study considering follow-up data collection completion status at years 1, 2, 5, 10, and 15.
In univariable analyses, multiple factors were associated with loss to follow-up (LOFU) including being a member of a socially disadvantaged group, substance use history, residence, payor, cause of injury, and results of earlier follow-up attempts. In a multiple logistic regression analysis examining the prediction of follow-up condition at 10 or 15 years post-injury, only payor and race/ethnicity were significant predictors. Hispanic ethnicity was associated with higher odds of LOFU, and these participants often spoke Spanish and were born outside of the United States.
The findings suggest a need to understand sociodemographic variables and their influence on participant attrition in longitudinal TBI research. With a better understanding of these predictors, procedures can be developed to address retention of participants who are identified as being at increased risk for study drop out.