A Natural Experiment Design Testing the Effectiveness of the IOP-29 and IOP-M in Assessing the Credibility of Reported PTSD Symptoms in Belgium

Sometimes forensic psychologists are asked to determine whether the symptoms of PTSD presented by the plaintiff are genuine or feigned. To this end, they may use both symptom validity tests (SVTs) and performance validity tests (PVTs), but SVTs are used far more frequently in these assessments. Thus, we conducted a natural experiment and administered an SVT (i.e., the IOP-29) and a PVT (i.e., the IOP-M) to 76 individuals instructed to feign PTSD and to 34 controls who self-reported exposure to a devastating flood several months earlier. The results confirm the utility of both measures in detecting feigned PTSD.