Capturing abnormal personality with normal personality inventories: an item response theory approach.

Correlational and factor-analytic methods indicate that abnormal and normal personality constructs may be tapping the same underlying latent trait. However, they do not systematically demonstrate that measures of abnormal personality capture more extreme ranges of the latent trait than measures of normal range personality. Item Response Theory (IRT) methods, in contrast, do provide this information. In the present study, we use IRT methods to evaluate the range of the latent trait assessed with a normal personality measure and a measure of psychopathy as one example of an abnormal personality construct. Contrary to the expectation that the measure of psychopathy would be more extreme than the measure of normal personality traits, the measures overlapped substantially in terms of the regions of the latent trait for which they provide information. Moreover, both types of inventories were limited in terms of measurement bandwidth, such that they did not provide information across the entire latent trait continuum. Implications and future directions are discussed.