title: Systematic bias in traumatic brain injury outcome studies because of loss to follow-up.
abstract: OBJECTIVE
  To identify potential sources of selection bias created by subjects lost to follow-up in studies of traumatic brain injury (TBI).
  
  
  METHODS
  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.
  
  
  METHODS
  Three prospective, longitudinal data sets-a single center, a multicenter, and a statewide incidence surveillance system and follow-up registry.
  
  
  METHODS
  Adolescents and adults hospitalized with a diagnosis of TBI.
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  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.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Ohio State University, Columbus, OH , USA. corrigan.1@osu.edu
authors.forename: John D
authors.initials: JD
authors.lastname: Corrigan
authors.forename: Cynthia
authors.initials: C
authors.lastname: Harrison-Felix
authors.forename: Jennifer
authors.initials: J
authors.lastname: Bogner
authors.forename: Marcel
authors.initials: M
authors.lastname: Dijkers
authors.forename: Melissa Sendroy
authors.initials: MS
authors.lastname: Terrill
authors.forename: Gale
authors.initials: G
authors.lastname: Whiteneck
mesh_terms: D000293:Adolescent; D000328:Adult; D015982:Bias; D001930:Brain Injuries / Q000453:epidemiology* / Q000534:rehabilitation*; D005500:Follow-Up Studies; D006760:Hospitalization; D006801:Humans; D016015:Logistic Models; D017063:Outcome Assessment, Health Care; D018579:Patient Selection; D012042:Registries; D015599:Trauma Severity Indices