Predictive validity of the PCL‐R for offenders with intellectual disability in a high security hospital: Treatment progress

Abstract

Background Among mainstream offenders, the severe personality disorder of psychopathy has considerable importance as a construct. The disorder has long been associated with failure to make treatment progress. Previous work has identified that psychopathy as a disorder occurs in samples of offenders with intellectual disability (ID), and suggests that the Psychopathy Checklist – Revised (PCL‐R: Hare, 1991, 2003) as a measure of the disorder has adequate reliability and validity (Morrissey et al., 2005). The present study aimed to compare the predictive power of the PCL‐R in relation to treatment progress with a more general assessment of violence risk, the HCR‐20 (Webster, Douglas, Eaves, & Hart, 1997).

Method A sample of 73 residents in a high security intellectual disability service, who had previously been assessed using the PCL‐R and the HCR‐20, were followed up at 2 years post‐assessment, and their outcome determined in terms of two distinct dichotomous variables reflecting definite positive treatment progress and definite negative treatment progress respectively.

Results In line with predictions, the PCL‐R Total score and Factor 1 score (Interpersonal and Affective aspects of psychopathy) and the HCR‐20 Total score were significantly inversely associated with a positive move from high to medium security hospital conditions within 2 years of assessment. However against prediction, the PCL‐R Total score had incremental validity over the HCR‐20. The PCL‐R Total and Factor 1, but not the HCR‐20 Total score, were also significantly associated with negative treatment progress in terms of a move to more restricted treatment conditions.

Conclusion Psychopathy, and in particular its interpersonal and affective manifestations, is a construct which appears to be associated with indirect measures of treatment progress in this high security ID group. However, caution should be applied in the use of a construct with potentially negative connotations in an already devalued population.

Keywords:

• Intellectual disability
• offenders
• psychopathy
• assessment

Notes

1. “Restricted” patients are detained under the Mental Health Act (1983) on a Hospital Order and have extra restrictions imposed on them.

2. An IQ cut‐off was not employed and therefore a small number of patients with IQ in the low to average range were included in the study. These patients were typically diagnosed with pervasive developmental disorders and had significant adaptive deficits which had led to their placement in ID services.

3. A score of 2 relates to a high PCL‐R score, a score of 1 to a moderate PCL‐R score, and a score of 0 to a low PCL‐R score.

4. Of these, 1 case had moved back to high security from medium security, 4 cases had moved to more secure settings within the hospital for further treatment, and 3 cases had been returned to prison for explicit reasons of untreatability.

5. This dichotomous variable defined whether the offence constituted “serious violence or sex”.

6. This was defined as all aggressive incidents recorded in the 12 months following initial assessment.

7. Other measures of accuracy associated with the ROC curve can be calculated, but for the purposes of this study only the AUC was examined.

8. Similar logistic regression analyses were not conducted for the outcome “negative progress” as the PCL‐R variables were the only variables which were found to predict this outcome significantly in both the correlational and ROC analyses.