Cross-validation of the PAI Negative Distortion Scale for feigned mental disorders: a research report

A major strength of the Personality Assessment Inventory (PAI) is its systematic assessment of response styles, including feigned mental disorders. Recently, Mogge, Lepage, Bell, and Ragatz developed and provided the initial validation for the Negative Distortion Scale (NDS). Using rare symptoms as its detection strategy for feigning, the usefulness of NDS was examined via a known-groups comparison. The current study sought to cross-validate the NDS by implementing a between-subjects simulation design. Simulators were asked to feign total disability in an effort to secure unwarranted compensation from their insurance company. Even in an inpatient sample with severe Axis I disorders and concomitant impairment, the NDS proved effective as a rare-symptom strategy with low levels of item endorsement that remained mostly stable across genders. For construct validity, the NDS was moderately correlated with the Structured Interview of Reported Symptoms-Second Edition and other PAI feigning scales. For discriminant validity, it yielded a very large effect size (d = 1.81), surpassing the standard PAI feigning indicators. Utility estimates appeared to be promising for both ruling-out (low probability of feigning) and ruling-in (high probability of feigning) determinations at different base rates. Like earlier research, the data supported the creation of well-defined groups with indeterminate scores (i.e., the cut score ± 1 SEM) removed to avoid high rates of misclassifications for this narrow band.