The TOMM1 discrepancy index (TDI): A new performance validity test (PVT) that differentiates between invalid cognitive testing and those diagnosed with dementia

Abstract

There is a need to develop performance validity tests (PVTs) that accurately identify those with severe cognitive decline but also remain sensitive to those suspected of invalid cognitive testing. The TOMM1 Discrepancy Index (TDI) attempts to address both of these issues. Veterans diagnosed with dementia (n = 251) were administered TOMM1 and the MSVT in order to develop the TDI (TOMM1 percent correct minus MSVT Free Recall percent correct). Cut offs based on the dementia sample were then used to identify those in the non-dementia sample (n = 1,226) suspected of invalid test performance (n = 401). Combining TOMM1 and the TDI in the dementia sample greatly reduced the false positive rate (specificity = 0.97) at a cut off of 28 points or less on the TDI. Those suspected of invalid testing were identified at much higher rates (sensitivity = 0.75) compared to the MSVT genuine memory impairment profile (GMIP, sensitivity = 0.49). By utilizing a neurologically plausible pattern of scores across two PVTs, the TDI correctly classified those with dementia and identified a large percentage with invalid test performance. PVTs utilizing a complex pattern of performance may help reduce one’s ability to fabricate cognitive deficits.