Abstract
The field of psychological injury and law is marked by use of psychometrically sound validity tests that use empirically derived cut scores to determine the credibility of cognitive deficits and psychological symptoms in forensic and related disability assessments (FDRA). Performance validity tests (PVTs) are used in neuropsychological/cognitive assessments to determine the extent to which test scores reflect true ability levels. Symptom validity tests (SVTs) are designed to evaluate the credibility of self-reported level of excessive report in behaviors, emotions, and thoughts. They monitor the rate of endorsement of rare, absurd, impossible, and improbable symptoms. The authors argue for a 30% rule as a tentative multivariate threshold for invalid presentation (with provisos). In other words, failure on about one third of the PVTs/SVTs administered should be required before deeming the overall profile non-credible to control for the threat of inflated false positive error due to the increasing number of instruments used. Typically, workers in the field use the multivariate threshold of ≥ 2 PVT failures in FDRA to deem an entire profile invalid, without considering the number of tests administered. The proposed 30% rule accommodates this face validity question. It is tentatively proposed as a starting point for future research, and with sufficient empirical support, a general guideline for FDRA.