Detecting Denial of Severe Psychiatric Disorder: An MMPI-2 Investigation of Criminal Defendants

Abstract

The ability of the MMPI-2 validity scales to differentiate mentally ill defendants who denied being mentally ill from mentally ill defendants who acknowledged their illness and those without mental illness was investigated. A stepwise logistic regression analysis (LGA) was utilized to identify the most parsimonious set of predictors among the MMPI-2 validity measures. The F and K scales and the Es-K index significantly differentiated the denying mental illness group from those acknowledging their psychiatric difficulties with a high degree of accuracy. An ROC curve utilizing the prediction scores from the LGA yielded an area under the curve of .89. An attempt to validate the model by differentiating the denial participants from those with no mental illness resulted in a marked decline in classification accuracy. The results are discussed in terms of the utility of the MMPI-2 in the detection of under reporting of psychiatric difficulties.