Systematic bias in traumatic brain injury outcome studies because of loss to follow-up.

OBJECTIVE To identify potential sources of selection bias created by subjects lost to follow-up in studies of traumatic brain injury (TBI). DESIGN Demographic, premorbid, injury-related, and hospital course characteristics were compared for subjects lost and found for 1- and 2-year postinjury follow-ups by using bivariate tests and logistic regression analysis. SETTING Three prospective, longitudinal data sets-a single center, a multicenter, and a statewide incidence surveillance system and follow-up registry. PARTICIPANTS Adolescents and adults hospitalized with a diagnosis of TBI. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Subjects were considered lost when no information was collected from the person with TBI or only limited information could be obtained from a proxy, for any reason, including death, refusal, inability to locate, and inability to interview. RESULTS At year 1 follow-up, 58.0% to 58.6% of subjects were found; 39.7% to 42.0% of subjects were found by year 2. Variables most frequently associated with loss to follow-up were cause of injury, blood alcohol level, motor function, hospital payer source, and race and ethnicity. CONCLUSIONS TBI follow-up studies may experience selective attrition of subjects who (1) are socioeconomically disadvantaged, (2) have a history of substance abuse, and (3) have violent injury etiologies. These phenomena are mitigated for those with more severe motor deficits. Loss to follow-up may be a problem inherent to this population; however, the high rate and its selective nature are problematic for outcome studies.