Influence of poor effort on neuropsychological test performance in U.S. military personnel following mild traumatic brain injury.

The purpose of this study was to examine the influence of poor effort on neuropsychological test performance in military personnel following mild traumatic brain injury (MTBI). Participants were 143 U.S. service members who sustained a TBI, divided into three groups based on injury severity and performance on the Word Memory Test and four embedded markers of poor effort: MTBI-pass (n = 87), MTBI-fail (n = 21), and STBI-pass (n = 35; where STBI denotes severe TBI). Patients were evaluated at the Walter Reed Army Medical Center on average 3.9 months (SD = 3.4) post injury. The majority of the sample was Caucasian (84.6%), was male (93.0%), and had 12+ years of education (96.5%). Measures included the Personality Assessment Inventory (PAI) and 13 common neurocognitive measures. Patients in the MTBI-fail group performed worse on the majority of neurocognitive measures, followed by the Severe TBI-Pass group and the MTBI-pass group. Using a criterion of three or more low scores <10th percentile, the MTBI-fail group had the greatest rate of impairment (76.2%), followed by the Severe TBI-Pass group (34.3%) and MTBI-pass group (16.1%). On the PAI, the MTBI-fail group had higher scores on the majority of clinical scales (p < .05). There were a greater number of elevated scales (e.g., 5 or more elevated mild or higher) in the MTBI-fail group (71.4%) than in the MTBI-pass group (32.2%) and Severe TBI-Pass group (17.1%). Effort testing is an important component of postacute neuropsychological evaluations following combat-related MTBI. Those who fail effort testing are likely to be misdiagnosed as having severe cognitive impairment, and their symptom reporting is likely to be inaccurate.