There is an extensive research literature on the association between
personality disorder, antisocial personality disorder, and risk of
future violent and sexual offences. Several studies have found an
elevated prevalence of personality disorder diagnoses amongst those
individuals with severe mental illness and criminal populations. While
there has been some work on the prevalence of personality disorder among
intellectual disability populations, it has been criticised as being
unreliable and inconsistent. The present authors have taken account of
these criticisms and recommendations in this comparison of 164 offenders
with intellectual disability across three settings – community,
medium/low secure, and high secure. In Study 1, DSM-IV diagnoses were
made on the basis of four information sources: file review, interview
with clinician, observations by care staff, and the Structured
Assessment of Personality Interview. Across the samples, total
prevalence of PD was 39.3%. The most common diagnosis was antisocial
personality disorder. There was a higher rate of diagnosis in the high
security setting, with no significant differences between the other two
settings. There was no diagnosis of dependent PD, indicating that
assessors were not overly influenced by the developmental disability
itself. In Study 2 it was found that increase in severity of PD (as
indicated by PCL-R scores and/or the number of PD diagnoses) showed a
strong lawful relationship with instruments predicting future violence
(VRAG, RM 2000/V) and a weaker relationship with instruments predicting
future sexual offences (Static-99, RM 2000/S). The results indicate the
utility of PD classification in this client group and that a number of
individuals with PD classification are being managed successfully in
community settings. These findings have considerable implications for
staffing, both in terms of which individuals can be treated by these
services and staff training.