Symptom Versus Performance Validity in Patients with Mild TBI: Independent Sources of Non-credible Responding

This study was designed to examine the relative contribution of symptom (SVT) and performance validity tests (PVTs) to the evaluation of the credibility of neuropsychological profiles in mild traumatic brain injury ( m TBI). An archival sample of 326 patients with m TBI was divided into four psychometrically defined criterion groups: pass both SVT and PVT; pass one, but fail the other; and fail both. Scores on performance-based tests of neurocognitive ability and self-reported symptom inventories were compared across the groups. As expected, PVT failure was associated with lower scores on ability tests (η p 2 .042–.184; d 0.56–1.00; medium-large effects), and SVT failure was associated with higher levels of symptom report (η p 2 .039–.312; d 0.32–1.58; small-very large effects). However, SVT failure also had a marginal deleterious effect on performance based measures (η p 2 .017–.023; d 0.23–0.46; small-medium effects) and elevations on self-report inventories were observed in the context of PVT failure (η p 2 .026; d 0.23–0.57; small-medium effects). SVT failure was associated with not only inflated symptom reports but also distorted configural patterns of psychopathology. Patients with clinically elevated somatic and depressive symptoms were twice as likely to fail PVTs. Consistent with previous research, SVTs and PVTs provide overlapping, but non-redundant information about the credibility of neuropsychological profiles associated with m TBI. Therefore, they should be used in combination to afford a comprehensive evaluation of cognitive and emotional functioning. The heuristic value of validity tests has both clinical and forensic relevance.