Development and Validation of the False Disorder Score: The Focal Scale of the Inventory of Problems

This article introduces the Inventory of Problems (IOP)-a new, computerized, 181-item tool designed to discriminate bona fide from feigned mental illness and cognitive impairment-and presents the development and validation of its focal, feigning scale, the False Disorder Score (IOP-FDS). The initial sample included (a) 211 patients and 64 offenders who took the IOP under standard conditions, and (b) 210 community volunteers and 64 offenders who feigned mental illness. We split this sample into three subsamples. The first (n = 301) was used to select the variables to generate the IOP-FDS; the second (n = 148) scaled the IOP-FDS into a probability score; and the third (n = 100) tested its validity with an independent data set. In this third subsample, the IOP-FDS had sensitivity = .90, specificity = .80, and a greater area under the curve (AUC = .95) than the IOP-29 (.91). For 40 participants, the Personality Assessment Inventory (PAI) was available, too. Within this subgroup, the IOP-FDS outperformed the selected PAI validity scales (AUC = .99 vs. AUC ≤ .85).