Using Item Response Theory to Bridge the Measurement Gap Between Normal Personality and Psychopathy
Walton, Kate E.
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Permalink
https://hdl.handle.net/2142/82100
Description
Title
Using Item Response Theory to Bridge the Measurement Gap Between Normal Personality and Psychopathy
Author(s)
Walton, Kate E.
Issue Date
2005
Doctoral Committee Chair(s)
Roberts, Brent W.
Department of Study
Psychology
Discipline
Psychology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Psychology, Personality
Language
eng
Abstract
The focus of the present studies is on whether psychopathy is an extreme variant of normal personality or whether it is a qualitatively distinct disorder. Typical measures of normal personality focus on adaptive variants of traits, whereas measures of psychopathy were designed to assess maladaptive variants. Presumably neither type of measure provides information for the entire range of the continuum, from normal to abnormal. As a result, it becomes difficult, if not impossible, to determine whether normal personality traits and psychopathy lie on the same continuum. In the present studies, I used Item Response Theory to demonstrate that measures of both normal personality and psychopathy are indeed restricted in their measurement bandwidth. Furthermore, I demonstrated that such measurement restriction has implications for taxometric analyses such that erroneous detection of taxa can occur. Specifically, in a simulation study I generated data sets with known underlying structures, either with or without restricted measurement range. When the range was restricted, a taxon was detected even when the known underlying structure was dimensional. Next, in the first of two empirical studies, which included a sample of undergraduate students (N = 459), I confirmed my expectation that measures of psychopathy are indeed restricted in their measurement bandwidth and contain only highly difficult items. Contrary to my expectations, the measure of normal personality also contained a disproportionate number of highly difficult items. A subsequent taxometric analysis indicated that, contrary to prior findings, psychopaths do not represent a discrete taxon. In Study 2, which included a combined sample of undergraduate students and individuals receiving treatment in a substance abuse recovery center (N = 272), I added items to an existing measure of psychopathy to provide better coverage across the latent trait. Again, two different taxometric procedures indicated that psychopaths do not represent a discrete taxon. Implications, limitations, and future directions are discussed.
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