Kells, Mark (2011)
Ph.D. thesis, University of Birmingham.
Two psychometric assessments, developed for use with mainstream offenders of normal intelligence, measuring impulsivity and locus of control respectively, were adapted for use with offenders with an intellectual disability (ID). The language and sentence structures used were simplified, and the content of questions was changed to provide contexts that were familiar to detained offenders with ID. Data generated from the responses of 47 male offenders with ID indicated that both tools demonstrated good levels of reliability, in terms of internal consistency, test re-test reliability and correlations with other tools measuring related concepts . Both instruments were found not to differentiate detained offenders with ID (n=47) from two control groups of non-offenders with ID (n=2x46). In addition, an examination of the utility of the impulsivity tool in predicting institutional aggression using receiver operator characteristics, was examined. Two risk assessments, the PCL-R (Hare, 2003) and the HCR-20 (Webster, Douglas, Eaves & Hart, 1997), were also included in this study. The results indicated that the impulsivity measure did not predict institutional aggression. However, the HCR-20 and its sub-scales and the PCL-R and its factors both provided moderate and strong predictive ability, particularly in relation to physical aggression.
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