Objective: The present study aims to evaluate the classification accuracy and resistance to coaching of the Inventory of Problems-29 (IOP-29) and the IOP-Memory (IOP-M) with a Spanish sample of patients diagnosed with mild traumatic brain injury (mTBI) and healthy participants instructed to feign. Method: Using a simulation design, 37 outpatients with mTBI (clinical control group) and 213 non-clinical instructed feigners under several coaching conditions completed the Spanish versions of the IOP-29, IOP-M, Structured Inventory of Malingered Symptomatology, and Rivermead Post Concussion Symptoms Questionnaire. Results: The IOP-29 discriminated well between clinical patients and instructed feigners, with an excellent classification accuracy for the recommended cutoff score (FDS ≥ .50; sensitivity = 87.10% for coached group and 89.09% for uncoached; specificity = 95.12%). The IOP-M also showed an excellent classification accuracy (cutoff ≤ 29; sensitivity = 87.27% for coached group and 93.55% for uncoached; specificity = 97.56%). Both instruments proved to be resistant to symptom information coaching and performance warnings. Conclusions: The results confirm that both of the IOP measures offer a similarly valid but different perspective compared to SIMS when assessing the credibility of symptoms of mTBI. The encouraging findings indicate that both tests are a valuable addition to the symptom validity practices of forensic professionals. Additional research in multiple contexts and with diverse conditions is warranted.
Keywords: Feigning & malingering; IOP-29 & IOP-M; SVT & PVT; experimental malingering; symptom validity.