Internal consistency and factor structure of personality disorders in a forensic intellectual disability sample

The publication of the DSM-III (American Psychiatric Association (APA), 1980) prompted a significant increase in interest and research on personality disorder (PD), and the concept has subsequently been incorporated into mental health legislation in the developed world. Despite this, such research on people with intellectual disability (ID) has been sporadic, with widely varying results. The present study addresses a number of criticisms directed at previous research.

DSM-IV (APA, 2000) diagnoses of PD were made on 164 participants with ID on the basis of four independent sources of classification.

Reliability data for each PD was acceptable and alpha was .74 or above, with the exception of schizotypal PD (.63). Exploratory and confirmatory factor analyses were conducted, with the former revealing a 4-factor solution accounting for 58.9% of the variance, and a 2-factor solution accounting for 37.2% of the variance emerging for the latter. The factors were orthogonal, and we called the first factor "avoidant/rumination/inhibited" and the second factor "acting out".

We review these findings in relation to previous research on PD and alternative frameworks for the understanding of personality. We hypothesise consistencies between these findings and previous work on personality and ID. A number of drawbacks to the research are discussed, including a caution on the pejorative nature of a diagnosis of PD in an already devalued population.