title: Mild traumatic brain injury meta-analyses can obscure individual differences.
abstract: OBJECTIVE
  Several published meta-analyses indicate that mild traumatic brain injury (MTBI) is associated with a favourable course of recovery over a period of days-to-weeks, with no indication of permanent impairment on neuropsychological testing by 3 months post-injury in group studies. These meta-analyses provide important but not definitive information relating to outcome from MTBI in individual patients. The purpose of this paper was to illustrate that a sub-group of patients with residual cognitive deficits could exist, yet be obscured using group inferential statistics.
  
  
  RESULTS
  A sample of 30 concussed amateur athletes and a hypothetical sample of 30 adults who had sustained MTBIs were used to illustrate these statistical issues. In both groups, a minority of subjects with residual cognitive deficits were not identified using group statistics.
  
  
  CONCLUSIONS
  It is important to appreciate that MTBI meta-analyses represent an aggregation of effect sizes derived from multiple groups across multiple studies. Therefore, this methodology could, theoretically, obscure small sub-group or individual effects. Implications for interpreting meta-analyses are discussed.
authors.affiliation: Department of Psychiatry, University of British Columbia, Vancouver, BC, Canada. giverson@interchange.ubc.ca
authors.forename: Grant L
authors.initials: GL
authors.lastname: Iverson
mesh_terms: D000328:Adult; D056352:Athletes; D001924:Brain Concussion / Q000150:complications* / Q000175:diagnosis; D003072:Cognition Disorders / Q000175:diagnosis / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D015201:Meta-Analysis as Topic; D009483:Neuropsychological Tests; D020127:Recovery of Function