Predictors of follow-up completeness in longitudinal research on traumatic brain injury: findings from the National Institute on Disability and Rehabilitation Research traumatic brain injury model systems program

Objective: To identify baseline participant variables in the domains of demographics, medical/psychosocial history, injury characteristics, and postinjury functional status associated with longitudinal follow-up completeness in persons with traumatic brain injury (TBI) using the TBI Model Systems (TBIMS) National Database (NDB).

Design: Exhaustive chi-square automatic interaction detection was used to identify factors that classified participants according to level of follow-up completeness.

Setting: Retrospective analysis of a multi-center longitudinal database.

Participants: Individuals (N=8249) enrolled in the TBIMS NDB between 1989 and 2009 who were eligible for at least the first (year 1) follow-up up to the fifth (year 15) follow-up.

Interventions: None.

Main outcome measures: Follow-up completeness as defined by 6 different longitudinal response patterns (LRPs): completing all follow-ups, wave nonresponse, dropping out, completing no follow-ups without formally withdrawing, formally withdrawing before completing any follow-ups, and formally withdrawing after completing some follow-ups.

Results: Completing all follow-ups was associated with higher levels of education, living with parents or others, and having acute care payer data entered in the NDB. Subgroups more vulnerable to loss to follow-up (LTFU) included those with less education, racial/ethnic minority backgrounds, those with better motor functioning on rehabilitation discharge, and those for whom baseline data on education, employment, and acute care payer were not collected. No subgroups were found to be more likely to have the LRPs of dropping out or formal withdrawal.

Conclusions: These data identify subgroups in which retention strategies beyond those most commonly used might reduce LTFU in longitudinal studies of persons with TBI, such as the TBIMS, and suggest future investigations into factors associated with missing baseline data.