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Introduction
Early studies on personality disorder (PD) and people with intellectual disabilities (ID) noted that, similar to studies in the general population, there was likely to be comorbidity with other mental disorders and illnesses (Earl, 1961; Blackburn, 2000). One of the first systematic investigations into PD and ID was conducted by Corbett (1979). He identified a prevalence rate of 25.4%, of which almost half was immature and unstable PD. The extent to which one can separate the effects of developmental delay as a result of ID from immature and unstable personality illustrates some of the difficulties inherent in the diagnosis of PD. Eaton and Menolascino (1982) reported a prevalence rate of 27% for PD in a community-based sample of people with ID. Ballinger and Reid (1987) used the Standardized Assessment of Personality (SAP; Mann et al., 1981) and reported a prevalence rate of severe PD in 22% of a sample of individuals with mild or moderate ID. These authors, along with Gostasson (1987), also commented on the difficulty in applying diagnostic criteria for PD to individuals with severe and profound ID. Early studies established that PD could be assessed and was prevalent to some extent in this population. They identified some of the difficulties concerning comorbidity and diagnosis in more severe levels of ID and pointed out some confusion with immaturity and dependence.
Khan et al. (1997) also used the SAP and reported that 50% of their sample had personality abnormalities and 31% had a degree of impairment sufficient to warrant a diagnosis of PD. Of those diagnosed, the specific disorders were as follows: schizoid 10%; impulsive 7%; paranoid 5%; dependent 3%; dissocial 3%; histrionic 1%; anxious 1%; and ankastic 1%. Goldberg et al. (1995) reported very high levels of PD in people with ID. They found abnormal personality traits in 57% of individuals in an institutional sample and 91% of individuals in a community sample.
Flynn et al. (2002) studied a hospital inpatient sample and reported that 92% were diagnosed with PD using ICD-10 criteria. In contrast, working with the same ICD-10 criteria, Naik et al. (2002) found PD in 7% of a community sample, while Alexander et al. (2002) found PD in 58% of a sample of patients referred to a forensic hospital.
A turning point in research on PD and ID came with Alexander and Cooray’s (2003) review of studies. They noted that there was a lack of reliable diagnostic instruments, the use of different diagnostic systems, a confusion of definition and personality theory, and difficulty in distinguishing PD from other problems integral to ID, such as communication problems, sensory disorders, and developmental delay. They concluded that “the variation in the co-occurrence of PD in ID with prevalence ranging from less than 1% to 91% in a community sample and 22% to 92% in hospital settings, is very great and too large to be explained by real differences.” They recommended tighter diagnostic criteria and greater use of behavioral observation and informant information. Reid et al. (2004) made similar recommendations and made initial attempts to integrate mainstream work on personality with the small amount of work available investigating PD and ID. These authors used the NEO-PI-R, the standard questionnaire measure of the Five Factor Model (FFM) of personality structure (Costa and McCrae, 1985). This is one of the most widely accepted assessments for personality, with considerable empirical support. It has also been one of the bases for the alternative model to assess PD in DSM-5. In a series of case illustrations, Reid et al. (2004) found that those individuals who scored high on psychopathy (Psychopathy Checklist–Revised; Hare 1991) had low scores on the agreeableness and conscientiousness scale of the NEO-PI-R. This finding is similar to that reported in mainstream personality research (Blackburn 2000).
Lindsay et al. (2005) employed the recommendations made by Alexander and Cooray (2003) in a study of 164 males with ID in three forensic settings – high-secure, medium/low-secure, and community forensic services. They employed four independently rated measures of PD: a DSM-IV criteria checklist completed, firstly, from file review; secondly, by a clinician; thirdly, from nurse observations; and, finally, the SAP completed by care staff. A consensus rating was derived from the four assessments and a total prevalence of PD in this forensic sample was 39.5%. They reported that the ratings had high levels of reliability. As would be expected in a forensic population, antisocial PD was the largest category at 22% of cases, and rates of PD across the other categories were between 1% and 3%. It should be noted that care was taken in these guidelines to avoid the confusion first mentioned by Corbett (1979), that of confusing developmental delay with immature or dependent PD. There were no cases with dependent PD in the entire sample. It is also interesting that a previous, more general, file review of mental disorder in this sample (Hogue et al. 2006) had found PD recorded at 22.6% in the case files. By far the highest level of under-recording was in the community forensic sample, which was 1.4% in the case files and 33% in the carefully organized assessment study (Hogue et al. 2006). These authors noted that even the highest figures found in this forensic ID sample were lower than the figures of over 90% in studies on community samples reviewed by Alexander and Cooray (2003).
Lindsay et al. (2007) reported a factor analysis of the PD categories. In mainstream PD research, Blackburn et al. (2005) had previously investigated higher-order dimensions with 168 male forensic psychiatric patients and found two higher-order factors that appeared to underlie personality structure. They labeled these two factors as “acting-out” and “anxious-inhibited,” which was similar to higher-order structures identified by Morey (1988). In a similar confirmatory factor analysis on offenders with ID, Lindsay et al. (2007) produced a two-factor solution similar to that found previously with an “avoidant/inhibition” factor with high loadings from schizotypal PD, avoidant PD, obsessive-compulsive PD, and a lower loading from schizoid PD; and an “acting-out” factor with high loadings from borderline, narcissistic, and paranoid PD, with a smaller loading from antisocial PD. Therefore, the higher-order dimensions of PD in this study (Lindsay et al., 2007) in forensic participants with ID were similar to those found in populations with mental disorder found in other studies (Blackburn et al., 2005).
Alexander et al., (2006) reported on the outcome of 65 patients with ID treated in medium-secure forensic hospital settings. They found that the main associations with reconviction were a previous offense of theft or burglary, age of less than 27 years, and the presence of a PD. This relationship between PD and crime has been shown repeatedly with mainstream offending populations (Monahan et al., 2001; Fazel and Danesh, 2002). Indeed, one of the main reasons promoting the study of PD has been, on the one hand, the predictive relationship between antisocial PD and crime, while, on the other, the predictive relationship between borderline PD and psychiatric patient status (Widiger and Frances, 1989). Using the same population as Lindsay et al. (2006), Morrissey et al. (2007) found that the Psychopathy Checklist–Revised (PCL-R) was significantly associated with negative treatment progress in terms of a move to more restricted treatment conditions. The PCL-R is strongly associated with antisocial PD. These authors have consistently made the caution that the construct of PD is a highly devaluing label and should be used very carefully with the population of people with ID who are already highly devalued.
Most of the more recent work on PD and ID has been done on forensic populations. Alexander et al. (2010) compared the progress of 138 patients with ID in a secure setting over a six-year period, 77 with a dissocial or emotionally unstable PD (ICD-10) and 61 without. They found that previous histories of aggression and violence were no different in the two groups, but convictions for violent offenses and compulsory detentions were significantly more common in the group with PD. However, there were no clinically significant differences in terms of outcome for the groups, and the authors concluded that patients with PD and ID could be successfully treated in a general service for people with ID and a range of mental disorders. In a further comparison, Alexander et al. (2012) compared the progress of three groups following treatment in a secure hospital system, one with ID, a second with ID and PD, and a third with PD only. The two groups with ID appeared to follow similar treatment and management trajectories, while the group with PD followed a very different trajectory. Both ID groups had lower rates of post-release conviction and lower rates of violent reoffenses at two-year follow-up.
Three small treatment studies have used an adapted version of dialectical behavior therapy (DBT) in small groups of people with ID. Sakdalan et al. (2010) used a 13-week program with six participants and, although the sample size was very small, they found significant improvements on dynamic risk assessment. Morrissey and Ingamells (2011) developed a longer 60-session DBT program and reported anecdotal improvements in four out of six participants, 12 months following treatment. Mason (2007) reported a single case where assessment of personality and PD guided successful treatment.
The assessment of personality and people with ID
The authors of DSM-5 have considered carefully the relationship between PD and normal personality, concentrating exclusively on the FFM of personality (McCrae and Costa, 1991). Beginning with Cattell (1946), factor models were developed and refined, with five robust factors emerging most consistently (Norman, 1963; Goldberg., 1981; McCrae and Costa, 1987). These factors are extraversion/introversion, agreeableness, conscientiousness, neuroticism, and openness to experience, and the FFM is a comprehensive statistical summary of personality traits.
The FFM of personality assumes a trait theory perspective, in that individual differences characterize a person, and these, in turn, will influence thoughts, feelings, and behaviors (McCrae and Costa, 1991). The five factors are thought to be fully comprehensive and generally agreed to be the basic dimensions of a “normal” personality (Emmons, 1995). Neuroticism (N) is the most consistent domain and runs on a continuum from neurotic to stable. A tendency to feel negative affect, for example, fear, guilt, or anger, is at the core of N. Extraversion (E) runs on a continuum from extraversion to introversion. E is sometimes known as the “sociable” domain; however, it also includes factors such as sensation-seeking and assertiveness, which do not necessarily have a sociable component. Openness (O) refers to the individual’s openness to experience and covers a wide range of attributes including intellect, imagination, and values. The Agreeableness (A) domain focuses most strongly on interpersonal abilities and needs, and runs on a continuum from agreeable to disagreeable. Conscientiousness (C) reflects determination, strong will, and a sense of duty, and is also related to some aspects of N such as impulse control and self-regulation factors (Piedmont and Weinstein, 1993; Costa and McCrae, 1995).
The NEO-PI-R is the most widely accepted and evaluated questionnaire measuring the FFM (Berry et al., 2001), which is the model employed for the alternative diagnostic system in DSM-5. The 241 questions of the NEO-PI-R thoroughly identify the five factors/domains and also the 30 facets which are the defining traits of the domains. The six facets of each domain are grounded in psychological theory and ensure that the domain is widely covered, and that they highlight key individual differences. N’s facets are anxiety, anger, hostility, depression, self-consciousness, impulsiveness, and vulnerability. The facets identified with E are warmth, gregariousness, assertiveness, activity, excitement seeking, and positive emotions. O’s facets were recognized as being fantasy, aesthetics, feelings, actions, ideas, and values. Trust, straightforwardness, altruism, compliance, modesty, and tender-mindedness are facets of A. Finally, C’s facets have been identified as competence, order, dutifulness, achievement, striving, self-discipline, and deliberation. It has been suggested by Roepke et al. (2001) that personality profiles are fairly stable over time, and there is little difference in the profiles of adults aged 50–84 and 85–100. After some criticism regarding the lack of validity scales within the NEO-PI-R (for example, Schinka et al., 1997), Costa and McCrae (1995) included an observer rating (form R) to be taken in addition to the self-rating (form S), which they believe reveals the validity of the responses. This also provides strength for work on people with ID in that there is a check on the self-ratings and also allows comparisons of both sets of results.
Lindsay et al. (2007) adapted and simplified the language of the NEO-PI-R to be suitable for people with ID. They first tested that the adapted assessment produced results very similar to the full questionnaire. They then used the self- and observer versions to assess its applicability for the client group with 40 participants with ID and carers who knew the person well. They found that there were consistent differences between self- and observer ratings, with people with ID rating themselves as significantly more agreeable, extraverted, and conscientious than observers. The difference was less marked in extraversion/introversion where the self-ratings were 5 percentiles above the mean and the observer ratings were 5 percentiles below the mean. However, with the A and C factors, observers rated the participant significantly lower in agreeableness and conscientiousness than the people with ID did themselves.
Given the extent of work on these various models of personality in mainstream literature, it is of surprise that research in the field of personality and ID has developed from an entirely different standpoint. The standpoint of all previous work has been, on the one hand, developmental, reviewing the way in which developmental experiences form personality characteristics in individuals with ID, and, on the other hand, the personality factors behind the way in which people with ID are motivated to interact with their environment. Therefore, in a series of studies with children, Switzky (2001) reviewed the importance of intrinsic motivation in children who worked harder, required less praise for staying on task, and maintained their performance longer when compared with externally motivated children, when working under self-monitored conditions. By contrast, externally motivated children worked better when under closer supervision by teachers. They concluded that self-regulation was an extremely important trait in people with ID when considering relatively independent living in less regulated settings. They felt that motivational orientation (intrinsic vs. extrinsic) was a central concept in personality development in individuals with ID. In a series of studies, (for example, Switzky and Haywood, 1991, 1992) it was found that these differences were most prevalent when there was less external support and guidance. Intrinsically motivated individuals worked as well in situations of higher supervision as they did in lower supervision situations.
In another model, Reiss and Havercamp (1997) outlined 16 basic values that provide motivation for all individuals, including people with ID. They developed an assessment to use these values, and Reiss and Havercamp (1997, 1998), in factor analytic studies, found a 16-factor solution that conformed to the basic values in their theoretical construction. They also found that people with and without ID showed the same motivational profiles in relation to achieving these basic values. In other words, people with and without ID pursue happiness through motivation for the same needs, which they specified as social contact, curiosity, honor, family, independence, power, order, idealism, status, vengeance, romance, exercise, acceptance, tranquillity, eating, and saving. Aberrant environments that did not satisfy ordinary desires and psychological needs are likely to produce personality difficulties, while aberrant motivation (for example, desire for excessive amounts of positive reinforcement) is similarly likely to result in distortions of personality.
A further personality approach based on a developmental perspective is that of Zigler and colleagues (Zigler 2001; Zigler et al. 2002), who have derived an alternative personality structure based on informant reports. Incorporating earlier developmental work, Zigler et al. (2002) described five traits as follows: positive reaction tendency (“heightened motivation … to both interact with and be dependent upon a supportive adult”); negative reaction tendency (“initial wariness shown when interacting with strange adults”); expectancy of success (“the degree to which one expects to succeed or fail when presented a new task”); outer directedness (“tendency … to look to others for the cues to solutions of difficult or ambiguous tasks”); and efficacy motivation (“the pleasure derived from tackling and solving difficult problems”). When compared with their typically developing peers, people with ID tend to have lower expectancy of success and efficacy motivation, and higher positive and negative reaction tendencies and outer directedness.
These conceptualizations of development and motivation are interesting and wide-ranging in their view of personality, but clearly quite distinct from the way in which personality theory has developed in mainstream populations.
We have reviewed these systems of personality assessment because normal personality has been a focus for the DSM-5 alternative system of classification. As mentioned, DSM-5 has emphasized the primary assessment system – the FFM. While there is little research on this system in people with ID, it is the case that there is a wealth of disparate research on personality and very little research substantiating the use of the FFM with this population.
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