The Myth of High False-Positive Rates on the Word Memory Test in Mild TBI

Abstract

This study was designed to replicate previous reports of elevated false-positive rates (FPR) on the Word Memory Test (WMT) in patients with mild traumatic brain injury (TBI) and to evaluate previous claims that genuine memory deficits and non-credible responding are conflated on the WMT. Data from a consecutive case sequence of 170 patients with mild TBI referred for neuropsychological assessment were collected. Failure rate on the WMT was compared to that on other performance validity tests (PVTs). The clinical characteristics and neuropsychological profiles of patients who passed and those who failed the WMT and other PVTs were compared. Base rate of failure was the highest on the WMT (44.7%), but comparable to that on other established PVTs (39.4–41.8%). The vast majority of patients (94.7%) who failed the WMT had independent evidence of invalid performance, refuting previous estimates of 20–30% FPR. Failing the WMT was associated with globally lower scores on tests measuring various cognitive domains. The neurocognitive profile of individuals with invalid performance was remarkably consistent across various PVTs. Previously reported FPR of the WMT were not replicated. Failing the WMT typically occurred in the context of failing other PVTs too. Results suggest a common factor behind non-credible responding that is invariant of the psychometric definition of invalid performance. Failure on the WMT should not be discounted based on rational arguments unsubstantiated by objective data. Inferring elevated FPR from high failure rate alone is a fundamental epistemological error.