Ecological Validity of the Inventory of Problems-29 (IOP-29): an Italian Study of Court-Ordered, Psychological Injury Evaluations Using the Structured Inventory of Malingered Symptomatology (SIMS) as Criterion Variable

• DOI: 10.1007/s12207-019-09368-4
• Publication Date: 2019-12-07T05:00:26Z
• Authors: Paolo Roma; Luciano Giromini; Franco Burla; Stefano Ferracuti; Donald J. Viglione; Cristina Mazza
• Keywords: Malingering; Legal psychology; Ecological validity; Convergent validity; Incremental validity

The Inventory of Problems-29 (IOP-29; Viglione, Giromini, & Landis, Journal of Personality Assessment, 99(5), 534–544, 2017) is a 29-item, recently published, self-administered test aimed at assessing the credibility of various symptom presentations. Although available research strongly supports the use of this symptom validity test in malingering-related contexts, to date, only few studies have analyzed data from real-life forensic evaluations. To fill this gap and explore ecological and convergent validity, the current study analyzed data from 74 court-ordered evaluations aimed at establishing the possible presence of psychological injury. Such evaluations are high-stakes situations in which exaggeration or malingering occur relatively often. We used a research-supported and popular symptom validity test, i.e., the Structured Inventory of Malingered Symptomatology (SIMS; Smith & Burger, Journal of the American Academy on Psychiatry and Law, 25:180–183, 1997), as our criterion variable. The IOP-29 produced excellent area under the curve (AUC) values of .98 with a recommended SIMS total score cutoff (≥ 17) and .99 when eliminating too-close-to-classify cases (Rogers & Bender, 2018) and very large Cohen’s d effect sizes of 2.98 and 3.59, respectively. Crucially, when implementing established cut scores from previous research, the IOP-29 yielded very high specificity and sensitivity rates, and the predictions from the two tests were strikingly similar. Taken together, these findings support the strong convergent validity of the IOP-29 and its utility in applied clinical and forensic settings.