This study examined intra-individual variability in a large sample (n = 629) of individuals with a history of mild traumatic brain injury (mTBI) or TBI referred for neuropsychological evaluation. Variability was assessed using the overall test battery mean standard deviation (OTBM SD). We found a negative linear relation between OTBM and OTBM SD (r = -.672) in this sample with a history of neurologic pathology, indicating that the variability is inversely related to cognitive performance and contrary to what is observed in most normative data. Analyses revealed main effects for OTBM and OTBM SD across three TBI severity groups: loss of consciousness (LOC) <1 h, LOC 1 h-6 days, and LOC >6 days. These effects were found for both a valid performance group (no failed embedded validity measures; n = 504) and an invalid performance group (failed one or more embedded validity measures; n = 125). These findings support that cognitive intra-individual variability is increased uniquely by both neuropathology and suboptimal effort, there is a dose-response relationship between neuropathology and cognitive variability, and intra-individual variability may have utility as a clinical index of both.
Keywords: Dispersion; Intra-individual variability; Performance validity; Traumatic brain injury.