SVT Meets PVT: Development and Initial Validation of the Inventory of Problems – Memory (IOP-M)

Abstract

A growing literature indicates that to evaluate the credibility of a clinical presentation it would be optimal to rely on multiple sources of information, and use both symptom validity tests (SVTs) and performance validity tests (PVTs) whenever possible. In this paper, we present the development and initial validation of a PVT module designed to be used in combination with a free-standing SVT. Named Inventory of Problems – Memory (IOP-M), this new PVT module is given to the examinee immediately after completing the Inventory of Problems – 29 (IOP-29). It consists of a 34-item, two-alternative, forced-choice, implicit recognition test. Results from 360 nonclinical volunteers – 192 instructed to respond honestly (honest controls) and 168 instructed to feign mental illness (experimental simulators) – suggest that the IOP-M has the potential to yield incremental validity over using the IOP-29 alone. In fact, a series of hierarchical logistic regressions using group as criterion variable (0 = honest control; 1 = experimental simulator) and the IOP-29 and IOP-M as predictors showed that the models including both measures significantly improved classification accuracy over those including the IOP-29 only, Δχ2 ≥ 19.1, p < .01. When considering the optimal cut scores for each measure, only 6 of the 168 simulators (i.e., less than 4%) passed both the IOP-29 and IOP-M, and only 3 of the 192 honest responders (i.e., less than 2%) failed both. A closer examination of false positive classifications, however, revealed that the IOP-M could be prone to false positive errors in examinees with moderate to severe cognitive impairment.