A Clinical Comparison, Simulation Study Testing the Validity of SIMS and IOP-29 with an Italian Sample

The Inventory of Problems–29 (IOP-29) was recently introduced as a brief, easy-to-use measure of non-credible mental and cognitive symptoms that may be applied to a wide variety of contexts or clinical conditions. The current study compared its validity in discriminating bona fide versus feigned (via experimental malingering paradigm) psychopathology against that of the Structured Inventory of Malingered Symptomatology (SIMS). Specifically, 452 Italian adult volunteers participated in this study: 216 were individuals with mental illness who were asked to take the SIMS and IOP-29 honestly, and 236 were nonclinical participants (experimental simulators) who took the same two tests with the instruction to feign a psychopathological condition. Two main, broad categories of symptom presentations were investigated: (a) psychotic spectrum disorders and (b) anxiety, depression, and/or trauma-related disorders. Data analysis compared the effect sizes of the differences between the patients and experimental simulators, as well as the AUC and classification accuracy statistics for both the SIMS and IOP-29. The results indicate that the IOP-29 outperformed the SIMS, with the differences between the two tools being more notable within the psychotic (IOP-29 vs. SIMS: d = − 1.80 vs. d = − 1.06; AUC = .89 vs. AUC = .79) than within the anxiety, depression, and/or trauma related subgroup (IOP-29 vs. SIMS: d = − 2.02 vs. d = − 1.62; AUC = .90 vs. AUC = .86). This study also demonstrates that the IOP-29, with its single cutoff score, is generalizable culturally and linguistically from the USA (English) to Italy (Italian).