Classification accuracy of the word memory test genuine memory impairment index

The Word Memory Test (WMT) assesses non-credible performance in neuropsychological assessment. To mitigate risk of false positives among patients with severe cognitive dysfunction, the Genuine Memory Impairment Profile was derived. Only a modest number of investigations has evaluated classification accuracy among clinical samples, leaving the GMIP's accuracy largely uncertain. Accordingly, a simulation experiment evaluated the classification accuracy of the GMIP in a group of healthy individuals coached to simulate mild traumatic brain injury (TBI) related memory impairment on the WMT.

Eighty healthy individuals were randomly assigned to one of the four experimental groups. One group was provided superficial information concerning TBI symptoms (naïve simulators), another was provided extensive information concerning TBI symptoms (sophisticated simulators), and a third group was provided extensive TBI symptom information and tactics to evade detection by performance validity tests (PVT) (test-coached). An honest responding control group was directed to give their best performance. All participants were administered the California Verbal Learning Test-2 (CVLT-2) and the WMT.

Among the TBI simulators, 90% of the test-coached, 95% of the sophisticated simulators, and 100% of the naïve simulators were correctly classified as exaggerating memory impairment on the primary WMT indices. The simulator groups performed worse than the honest responding group on the CVLT-2. Of those who exceeded the WMT cutoffs, 60%, 27%, and 6% of the naïve-, sophisticated-, and test-coached simulators manifested the GMIP profile, respectively.

The GMIP is apt to misclassify individuals as having genuine memory impairment, especially if a naïve or unsophisticated effort is made to exert non-credible performance. Indeed, individuals who employ the least sophisticated efforts to exaggerate cognitive impairment appear most likely to manifest the GMIP. The GMIP should be used cautiously to discriminate genuine impairment from non-credible performance, especially among people with mild TBI.