The Russian IOP-29: A Validation-by-Replication Study in a Kazakhstan Community Sample

In legal contexts, psychiatric and psychological assessment decisions can have substantial consequences, so mental-health symptoms reported by evaluees must be assessed for credibility rather than taken at face value. To this end, the Inventory of Problems–29 (IOP-29) is particularly relevant because it was specifically developed to assess the credibility of self-reported symptoms and has been investigated in numerous language versions. Because no study had yet addressed the Russian-language IOP-29, this study replicated Akca et al.’s (2023) research paradigm in a Kazakhstan community sample. Overall, 154 volunteers completed the IOP-29 three times, yielding 462 administrations under honest responding, random responding, and instructed feigning conditions; the latter involved feigned schizophrenia, depression, or PTSD. The False Disorder Probability Score (FDS) discriminated feigned from honest responding, with specificity = 0.92 and sensitivity = 0.81 at the standard cutoff (FDS ≥ 0.50). The Random Responding Scale (RRS) differentiated random from non-random responding at the mean-score level, but classification accuracy was mixed. These findings provide support for the validity of the Russian IOP-29 as a measure of the credibility of reported mental health symptoms, whereas the RRS requires further study before it can be used routinely in applied settings.