The inventory of problems-29 (IOP-29) in a US clinical sample.

Objective

Research on the Inventory of Problems-29 (IOP-29) has primarily used simulation designs and non-US samples. This study evaluated the IOP-29 in US clinical samples relative to validity scales obtained from Minnesota Multiphasic Personality Inventory (MMPI). Method: Clinical patients (N = 217) were administered the IOP-29 and the second or third version of the Minnesota Multiphasic Personality Inventory (MMPI) as part of routine care. Correlations evaluated criterion validity of the IOP-29 False Disorder Probability Score (FDS). Diagnostic accuracy statistics were calculated, with the invalid group (n = 25) identified as those producing invalid scores on any two or more MMPI scales compared to those with no invalid scores.

Results

The IOP-29 was positively correlated to overreport scales (ρ = .24 to .62), and not or negatively correlated to underreport scales. At FDS ≥ .50, sensitivity was .72 at specificity of .88. To reach a specificity of .90, the cutoff score needed raised to .58, but without any change in sensitivity. At the more conservative ≥ .64, specificity raised to .95 but sensitivity dropped to .56.

Conclusions

The IOP-29 showed utility as a broad measure of negative response bias in mixed clinical sample in the US. The recommended cutoff of FDS ≥ .50 worked well in this mixed clinical sample, though a slight increase in cutoff was needed to achieve .90 specificity. The measure would benefit from additional criterion group studies in different clinical and forensic samples and using additional methods for identifying participants with invalid profiles.