Research in Developmental Disabilities 35 (2014) 2137–2147

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Research in Developmental Disabilities

Shifting impairment and aggression in intellectual disability and Autism Spectrum Disorder E.M. Visser a, H.J.C. Berger a, J.B. Prins a, H.M.J. Van Schrojenstein Lantman-De Valk b, J.P. Teunisse a,c,d,* a

Radboud University Nijmegen Medical Centre, Department of Medical Psychology, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands Radboud University Nijmegen Medical Centre, Department of Primary and Community Health Care, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands c Dr. Leo Kannerhuis, Centre for Autism, Department of Research & Development, P.O. Box 62, 6865 ZH Doorwerth, The Netherlands d HAN University of Applied Sciences, Research group Autism through the Lifespan, P.O. Box 6960, 6503 GL Nijmegen, The Netherlands b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 9 December 2013 Received in revised form 15 April 2014 Accepted 22 April 2014 Available online

Aggressive behaviour is a major problem in individuals with an intellectual disability (ID) as well as in individuals with an Autism Spectrum Disorder (ASD). There are indications that suggest a link between cognitive shifting and aggression. In this study, reports of aggressive incidents of adolescents and young adults with different clinical diagnoses (ID, ID + ASD, ASD) were collected during 1 year, using the Staff Observation Aggression ScaleRevised. Whether they were diagnosed with ID, ASD or both; individuals who displayed aggression were found to face more cognitive shifting difficulties than non-aggressive individuals, while no significant differences were found on severity of ASD symptoms. Study results support the assumption that a cognition-based model for aggression may be more adequate than a diagnose-based model. ß 2014 Elsevier Ltd. All rights reserved.

Keywords: Cognitive shifting Aggression Autism Intellectual disability

1. Introduction Aggression is frequently reported in the care for individuals with an intellectual disability (ID) and an Autism Spectrum Disorder (ASD). For instance, in a review on prevalence studies of aggressive challenging behaviour, Benson and Brooks (2008) report that aggression is a significant problem in individuals with ID, from childhood to adulthood and at all levels of intellectual impairment. Aggressive behaviour is defined as any verbal, non-verbal of physical behaviour that is threatening or causing harm to the client him- or herself, to others or to objects (Morrison, 1990). Incidence rates of aggression in ID vary between around 10% (Emerson et al., 2001; Holden & Gitlesen, 2006; Tyrer et al., 2006) till around 50% of study samples (Benson & Brooks, 2008; Crocker et al., 2006; Tenneij & Koot, 2008). In a large-scale study, Crocker et al. (2006) found that over half of 3165 adults with ID receiving services from rehabilitation departments in Quebec exhibited aggressive behaviour in 1 year, of which 24% were involved in property damage, 36.7% in verbal aggression and 24.4% in physical aggression. Several authors identify ASD as an added risk factor for aggressive challenging behaviour in ID (Brosnan & Healy, 2011; McClintock, Hall, & Oliver, 2003; Tsiouris, Kim, Brown, & Cohen, 2011). Aggression is more common among individuals

* Corresponding author: Tel.: +31 263333037. E-mail address: [email protected] (J.P. Teunisse). http://dx.doi.org/10.1016/j.ridd.2014.04.021 0891-4222/ß 2014 Elsevier Ltd. All rights reserved.

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with a dual diagnosis of ID and ASD (Brosnan & Healy, 2011; McClintock et al., 2003; Tsiouris et al., 2011), and more severe ASD is associated with higher rates of challenging behaviour (Matson & Rivet, 2008). Aggressive behaviour is not only a major issue in individuals with ID and ASD, but also in individuals with ASD, without ID. High prevalence rates of aggression have been reported in individuals with high functioning ASD (Kanne & Mazurek, 2011; Lerner, Haque, Northrup, Lawer, & Bursztajn, 2012; White, Ollendick, & Bray, 2011). Quek, Sofronoff, Sheffield, White, and Kelly (2012) examined the incidence of anger in young adults with Asperger’s syndrome and found that 17% of the participants reported clinically significant levels of anger. Aggression could be considered the most direct form of ASD symptoms and externalising problem behaviour, compared to other behavioural problems such as intrusive and destructive behaviour. General behavioural problems have an overall negative influence on parents and caregivers: it elicits stress in caregivers and leads to negative interactions between caregivers and their clients, which may result in a deterioration of the quality of care (Bromley & Emerson, 1995; Brosnan & Healy, 2011). Moreover, behavioural problems are linked to increased service costs because of raised staff sickness and turnover rates, higher investment in support and supervision and possible compensatory payments for injured staff (Allen, 2000). Yet, particularly the occurrence of aggressive incidents immediately causes a disturbance in caregivers’ well-being and everyday functioning, due to the direct perceived threat to personal safety (Brosnan & Healy, 2011) and feelings of shock, fear and anger (Kiely & Pankhurst, 1998). Reported failure in managing care for adults with ID rises from 10% when aggression is absent to 42% when clients do display aggression (Tyrer et al., 2006). For this reason, we will specifically concentrate on aggression in the present study. One of the factors that may increase the occurrence of aggressive incidents is an impairment in cognitive shifting. Cognitive shifting (also referred to as attentional set-shifting or cognitive/mental flexibility) is a component of executive functioning and refers to the ability to shift to different thoughts, actions and strategies when changes in a situation occur (Geurts, Corbett, & Solomon, 2009; Hill, 2004a). We have demonstrated in a previous article that it is possible to measure and differentiate cognitive shifting using the Wisconsin Card Sorting Test (WCST) and the Intra Dimensional/Extra Dimensional Task of the Cambridge Neuropsychological Test Automated Battery (CANTAB ID/ED), in individuals with ID as well as in those who additionally have an ASD diagnosis (Roelofs et al., in press). In a review on ERPs, fMRI and brain connectivity studies, Gomot and Wicker (2012) suggest that need for sameness and restricted, repetitive behaviours in ASD can be explained through stressful reactions and a sense of overstimulation triggered by unpredictable events. Indeed, shifting impairment is illustrated by perseverative, stereotyped behaviour and difficulty handling unexpected and changing situations (Hill, 2004a). Woodcock, Oliver, and Humphreys (2011) found a direct association between attention switching and temper outburst in individuals with Prader–Willi syndrome. Furthermore, shifting deficits have been linked to the number and the severity of violent offences in adolescent and adult delinquents (Hancock, Tapscott, & Hoaken, 2010; Pihet, Combremont, Suter, & Stephan, 2012), indicating that a rigid cognitive style may contribute to the expression of aggression. Several studies have found impairment in shifting to be central to ASD (Hill, 2004b; Russo et al., 2007; Sanders, Johnson, Garavan, Gill, & Gallagher, 2008). However, in an overview of studies concerning shifting in ASD, no consistent evidence for shifting impairment was found (Geurts et al., 2009). These inconsistent findings may be due to the heterogeneousness of ASD: individuals with ASD display varied and miscellaneous symptoms (American Psychiatric Association, 2000) and there are substantial differences in the type of difficulties they experience (Geurts et al., 2009). Teunisse, Cools, van Spaendonck, Aerts, and Berger (2001) have been able to create subgroups in ASD participants on basis of central coherence and cognitive shifting performance, implying that shifting impairment is present in some, but not all individuals with ASD. Though some authors describe a link between ASD symptom severity and aggression (Matson & Rivet, 2008; White et al., 2011), Kanne and Mazurek (2011) found that ASD symptom severity as assessed by clinicians was not associated with aggression. Likewise, in a previous study we did not find an association between ASD-symptoms and ratings of externalising problem behaviour, while shifting impairment was significantly correlated with externalising problem behaviour (Visser, Berger, Van Schrojenstein Lantman-De Valk, Prins, & Teunisse, Submitted). It proved to be possible to differentiate between individuals displaying severe behavioural problems and individuals displaying mild or no behavioural problems based on rated shifting, while this differentiation was not possible based on ID and ASD diagnosis (Visser et al., Submitted). In the current study we will analyse the possible association between ASD symptoms, shifting impairment and aggression through a different perspective: using observation-based registrations of aggression, we will compare participants who have exhibited aggression (the ‘aggressive group’) with participants of whom no aggressive incidents have been reported (the ‘non-aggressive group’) on shifting impairment and severity of ASD symptoms. In contrast to our previous study, we will not only include individuals with ID, with and without ASD, but also individuals with ASD, without ID. The aim of this study is to investigate whether individuals who display aggression face more shifting difficulties than non-aggressive individuals and to examine how both groups score on severity of ASD symptoms. Shifting will be measured using both neuropsychological tasks (the CANTAB ID/ED; Cambridge Cognition, 1996; and the WCST; Heaton, Chelune, Talley, Kay, & Curtiss, 1993) as well as two rating scales of shifting (the Behaviour Flexibility Rating Scale-Revised; Peters-Scheffer et al., 2008; and the BRIEF executive functioning questionnaire; Smidts & Huizinga, 2009), for the reason that these two types of instruments possibly measure different constructs (Mahone et al., 2002; Teunisse et al., 2012; Vriezen & Pigott, 2002). In addition to the main analyses, we will explore provocations that have led to aggression. Furthermore, we will examine differences between the three diagnostic groups (ID, ID + ASD, ASD) on severity of ASD symptoms, shifting impairment and externalising problem behaviour, in order to aid the interpretation of our main findings.

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2. Method 2.1. Subjects Participants consisted of individuals with ID, individuals with ID + ASD and individuals with ASD. Participants in the ID and ID + ASD group were included if their IQ-score fell within the mild intellectual disability range (50–69; American Psychiatric Association, 2000). According to the criteria of the Dutch Ministry of Health, Welfare and Sport for mental disability (Woittiez, Ras, & Odijk, 2012), participants with IQ scores in the borderline intellectual disability range (70–85) were also included, when they in addition had chronic and distinct impairments in adaptive social functioning, educational problems or behavioural difficulties. Individuals in the ASD group were included if their IQ-score fell at least within the normal range (higher than 85; American Psychiatric Association, 2000). When a congenital or acquired aetiology of ID was identified, like for instance fragile X, Williams or Down Syndrome, individuals were excluded from the study because these syndromes are known to be associated with specific weaknesses in cognitive ability (Carney, Brown, & Henry, 2013; Van der Molen et al., 2010). Individuals using medication known to have central effects, such as opioids or antipsychotics, were also excluded since medication acting on the dopaminergic system can influence cognitive shifting (Berger et al., 1989). Finally, individuals with sensory or motor disorders were excluded when these conditions could impede the performance on neuropsychological tasks. Individuals with ASD and ID + ASD, were diagnosed by experienced psychiatrists at the moment of their admission to the service providers. Diagnosis was given according to the criteria of an Autistic Disorder (299.00), Pervasive Developmental Disorder Not Otherwise Specified (299.80) or Asperger’s Disorder (299.81) by means of the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 2000). Participants with ID and ID + ASD were recruited from three Dutch service providers which offer care and treatment to people with intellectual disabilities: SIZA, Pluryn and Dichterbij. One participant was recruited from a centre for autism: Dr. Leo Kannerhuis. Participants with ASD were recruited from a treatment centre for adolescents with ASD: Yulius Autisme, de Steiger. The participating service providers indicated whether their clients met the above-mentioned criteria by using available intelligence scores. Fifty-five individuals with mild to borderline ID (IQ range 50–85) and 18 individuals with IQ in at least the normal range (IQ 85 or higher) were included in the study. Eighteen participants with ID and four individuals without ID were excluded from the listwise analyses, because of missing data on shifting, severity of ASD symptoms and externalising problem behaviour. Consequently, the diagnostic groups consisted of 17 individuals with ID, 20 individuals with ID + ASD and 14 participants with ASD. The age range of the 40 males and 11 females was 14–31 years; mean age was 20.5 (SD 4.9). The total study sample was divided into an ‘aggressive’ and a ‘non-aggressive’ group based on registrations of the Staff Observation Aggression Scale-Revised (SOAS-R; Nijman et al., 1999). An individual was defined as ‘aggressive’ if he or she was involved in at least one aggressive incident. Individuals without any SOAS-R registrations were defined as ‘non-aggressive’. All participants and their parents or caregivers provided informed consent and the engaged service providers gave their authorization. Participation was rewarded with a gift card of 10 Euro’s. This study was approved by the Committee on Research involving Human Subjects, region Arnhem/Nijmegen and was conducted in accordance with the World Medical Association Declaration of Helsinki (World Medical Association General Assembly, 2008). 2.2. Instruments 2.2.1. Intelligence The participating service providers had different preferences regarding methods and timing to test intelligence, thus the IQ scores provided by the service providers were not directly comparable. Therefore, the Form Board subtask of the Groninger Intelligence Test (GIT; Luteijn & Barelds, 2004) was included as an independent control measure of IQ. In this visuospatial task, participants were asked to indicate how two-dimensional figures fit into an outline. This non-verbal task was chosen in order to eliminate the potential negative influence of verbal impairments, which are frequently present in ASD. The Form Board subtask has been proven to be highly correlated with the total GIT-outcome and is therefore considered an accurate predictor of IQ (Luteijn & Barelds, 2004). Hence, using the GIT Form Board it was possible to check provided IQscores without overburdening the participants with an elaborate IQ-test which they already completed in some form at the moment of their admission. Form Board scores were found to be significantly correlated with total IQ scores provided by the service providers (Spearman’s rho = .80, p  .001, n = 44), which implies that GIT Form Board can be used as an overall IQ predictor in our study sample. Higher Form Board scores indicate higher overall intelligence. 2.2.2. Autistic symptoms We believed it would be of interest to examine severity of autistic symptoms in all participants, for the reason that individuals without ASD might also display these symptoms to some extent. Severity of autistic symptoms was quantified with a checklist of the 12 DSM-IV-TR (American Psychiatric Association, 2000) diagnostic criteria (sub A) for 299.00 autistic disorder (ABL; Berger, Aerts, Van Spaendonck, Cools, & Teunisse, 2003; Teunisse et al., 2001). Each criterion was reformulated into a positive statement (e.g. criterion A 1d: ‘‘able to show social or emotional reciprocity’’). This statement could be scored

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as ‘‘not impaired’’ (score 0), ‘‘slightly impaired’’ (score 1), ‘‘mildly impaired’’ (score 2), or ‘‘severely impaired’’ (score 3). The interrater reliability of the ABL total score was assessed by asking a psychologist and a psychiatrist to independently score 27 sets: Cronbach’s alpha = .86; p  .001 (Teunisse et al., 2001). In this study the ABL was found to be significantly correlated with scores on the Scale of Pervasive Developmental Disorders in Mentally Retarded Persons (PDD-MRS; Kraijer & De Bildt, 2005): Spearman’s rho = .78, p  .001, n = 50, which is an index for good convergent validity of the ABL. Higher scores on the DSM-IV-TR checklist reflect a higher severity of autistic symptoms (maximum 36). 2.2.3. Shifting In different studies a discrepancy has been found between neuropsychological executive functioning tasks and observational executive functioning ratings outcomes (e.g. Mahone et al., 2002; Teunisse et al., 2012; Vriezen & Pigott, 2002). Following Kenworthy, Yerys, Anthony, and Wallace (2008) who recommend a multi-source assessment to counteract difficulties measuring executive functions, it was decided to assess shifting using both neuropsychological tests and rating scales. Miyake, Emerson, & Friedman (2000) propose that reliability and validity problems of executive functioning tasks can be alleviated by administering multiple tasks for each executive function. Using a single task, it is impossible to differentiate trait variance from undesired method variance (Campbell & Fiske, 1959). With multiple measures, aggregation of the scores can be used to extract what is common among the tasks, resulting in a better measure of the targeted function. For that reason, two neuropsychological tests and two rating scales were used to measure shifting. 2.2.3.1. Neuropsychological tasks. The Wisconsin Card Sorting Test (WCST) is a measure of abstract reasoning that requires the ability to shift strategies (Berg, 1948; Heaton et al., 1993). The WCST has been validated in individuals with autism and learning disabilities (Ozonoff, 1995) and has previously been used to measure shifting in children with ID (Gligorovic & Buha, 2013) and in children with autism, with and without mild ID (Robinson, Goddard, Dritschel, Wisley, & Howlin, 2009). The original table-top, 128-card version was used. Participants were asked to sort cards according to a specific selection category (colour, shape or number), which the participant must induce from feedback on previous sortings provided by the examiner. Without the participants’ knowledge, the rule to match the response cards was changed after 10 correct sortings. In response, the participants were required to flexibly shift to another selection category. The test was discontinued when six categories were completed, or when the participant failed to detect a selection category within 24 trials. When the participant completed a category, the number of trials needed before making 10 consecutive correct sortings was counted. If the participant failed to complete a category, the maximum score of 24 was assigned to that category and all consecutive categories. Shifting was measured by the total number of trials needed to discover the sorting rule for all six categories. Higher scores on the WCST reflect poorer cognitive shifting (maximum 144). The Intra Dimensional/Extra Dimensional Task of the Cambridge Neuropsychological Test Automated Battery (CANTAB ID/ED) is a computerized task designed to measure shifting (Downess et al., 1989; Hughes, Russell, & Robbins, 1994). This non-verbal task systematically increases shifting demands, enabling precise identification of the locus of impairment (Cambridge Cognition, 1996; Hughes et al., 1994). Internal manipulations of the CANTAB ID/ED make it possible to control for other deficits, such as impaired inhibition (Cambridge Cognition, 1996; Hughes et al., 1994). The CANTAB has been studied in a wide range of clinical samples, providing strong support for a valid measurement of cognitive functions in adults (Luciana & Nelson, 2000). The task has frequently been used in individuals with ID of different ages and intellectual ability (see Yerys et al., 2009, for an overview). In this task, pink colour-filled shapes and white lines are used as stimuli. On a computer screen, four empty boxes are shown. At the start of each trail, the subject sees two colour-filled shapes and is instructed to select one. Through trial and error learning from computer feedback (‘correct’ or ‘wrong’), subjects must induce a selection rule. After six consecutive correct responses, the next trail starts and the rules are changed. The first seven stages of the test require intra-dimensional shifting (colour filled shapes remain the only relevant dimension), where in stages eight and nine extra-dimensional shifting is required (white lines become the only relevant dimension). For more detailed information on the CANTAB ID/ED task: see Yerys et al. (2009). The task was discontinued when the nine stages were completed or when the participant failed to complete a stage in less than 50 trials. In the latter case, the score on the remaining stages was replaced by the maximum score of 50. Shifting was measured by the total number of trials needed to complete all nine categories. Higher scores reflect poorer cognitive shifting capacities (maximum 450). 2.2.3.2. Rating scales. The Behaviour Flexibility Rating Scale-Revised (BFRS-R) is a tool for investigating flexibility in everyday functioning in individuals with developmental disabilities and has been validated in individuals with mild intellectual disability and autism (Green et al., 2008; Peters-Scheffer et al., 2008; Pituch et al., 2007). Items in this 16-item rating scale refer to a number of specific and unexpected events and changed routines that may prove problematic for the subject. The degree to which each situation would be a problem was rated on a 4-point scale ranging from 0 (no problem at all) to 3 (causes severe problems). Higher scores indicate poorer flexibility (maximum 48). The Behaviour Rating Inventory of Executive Function (BRIEF) was designed to measure subdomains of the executive function construct with ecological validity for clinical assessment (Gioia, Isquith, Guy, Kenworthy, & Baron, 2000; Smidts & Huizinga, 2009). The BRIEF has been proven to have clinical utility in individuals with ASD and mental retardation (Gioia

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et al., 2000; Gioia, Isquith, Retzlaff, & Espy, 2002). The 75 items describe various behaviours, classified into eight scales. For the purpose of this study the shifting domain was analysed. The frequency of each potentially problematic shifting behaviour was rated on a 3-point scale ranging from 1 (never), via 2 (sometimes) to 3 (often). Higher ratings reflect greater impairment in shifting (maximum 24). 2.2.4. Externalising Problem Behaviour Behavioural problems were assessed using a proxy-report instrument to measure psychopathology: the Adult Behaviour Checklist (ABCL 18-59; Achenbach & Rescorla, 2003). The ABCL has been found to be a reliable and valid measure in individuals with ID and ASD (Tenneij & Koot, 2007). The 123 problem items comprise an external as well as an internal problem scale. Only the externalising problem behaviour scale was used in this study, consisting of the subscales aggressive, rule-breaking and intrusive behaviour. The respondent is required to use a 3-item response scale: not true, somewhat/ sometimes true, and very often true. A higher score on externalising problem behaviour indicates more behavioural problems (maximum 70). 2.2.5. Aggression Aggressive incidents were recorded using the Staff Observation Aggression Scale-Revised (SOAS-R; Nijman et al., 1999), a tool measuring the prevalence, severity and determinants of aggression. The SOAS-R has been widely used in psychiatric wards and nursing homes (Nijman, Palmstierna, Almvik, & Stolker, 2005) but the use of this instrument in treatment facilities for people with ID is relatively new (Tenneij, Didden, Stolker, & Koot, 2009; Tenneij & Koot, 2008) and to our knowledge the SOAS-R has so far not been applied in the specific population of individuals with ID + ASD. The SOAS-R has been demonstrated to have fair to good interrater reliability and to correlate highly with other instruments for measuring of aggressive behaviour (Nijman et al., 2005; Steinert, Wolfle, & Gebhardt, 2000). The SOAS-R form consists of five columns that assess different aspects of the aggressive incident: (1) provocative antecedents of the incident, (2) means used during the aggression (verbal, physical, objects), (3) target of the aggression, (4) consequences for potential victims of the aggression and (5) the measures taken to stop the aggression. Since items in each column have boxes that can simply be tagged, aggressive incidents can be recorded quickly and easily. An aggressive incident entails a situation in which different behaviours against one or more targets can occur at the same time, triggered by numerous antecedents. Therefore, it is possible to tag multiple boxes per column on the SOAS-R form. We have used the SOAS-R version that has been developed specifically for residential care settings for individuals with ID (Nijman, 2005). Compared to the original version of the SOAS-R, the current version has more answer options to score provocations of aggression. 2.3. Procedure Tests were administered by a junior psychologist of the department of Medical Psychology of the Radboud University Medical Centre, who visited the participants in the facilities where they resided. Participants were tested individually in a closed and quiet environment. Rating scales considering the participants’ daily behaviour were handed out to the professional carers at the time of the test session. The professionals who filled out these rating scales were required to be involved in direct care for or counselling of the participant during at least 1 year. The BRIEF, BFRSR and the ABCL were completed by professional carers, on basis of daily observations of the participants’ behaviour. Completing rating scales regarding autism (PDD-MRS) and autistic symptoms (ABL) requires the ability to interpret participants’ behaviour with respect to ASD symptoms and thus were filled out by psychologists. In a few cases (9%) these rating scales were completed by professional carers because the involved psychologists were not sufficiently familiar with the participant’s behaviour. During 12 months, professional carers and psychologists were asked to fill out a SOAS-R form each time they were involved in or observed an aggressive incident entailing one or more study participants. 2.4. Statistical analyses All analyses have been carried out using SPSS 20.0 for Windows using raw scores of the variables. An overall rating-based composite score of shifting was obtained by taking the average of calculated z-scores of BRIEF and BFRS-R rating scales outcomes. Likewise, an overall neuropsychological task-based composite score of shifting was calculated by averaging zscores of WCST and CANTAB ID/ED task scores. T-tests and chi-square analysis were used to check whether there were differences in sex, age and intelligence between individuals who displayed aggression and individuals who did not. The main analyses included independent-sample t-tests in which differences on study measures were analysed between the two groups. Additionally, Pearson correlations were used to (a) examine the correspondence between the neuropsychological task-based and the rating-based composite score of shifting and (b) examine internal correspondence for the two neuropsychological tasks as well as for the two rating scales. Descriptive statistics were calculated for the provocative incidents of aggression. Finally, ANOVA and chi-square analyses were used to examine differences between the three diagnostic groups (ID, ID + ASD, ASD). Where necessary, post hoc pairwise comparisons were conducted using Fisher’s leastsignificance.

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2142 Table 1 Demographics.

Non-aggressive

Sex Male Female Age Intelligence

Aggressive

n

M

SD

n

M

SD

28 9 37 37

– – 21.1 9.6

– – 5.3 3.7

12 2 14 14

– – 18.9 9.3

– – 3.7 4.3

Note. Intelligence = intelligence as measured by GIT Form Board.

3. Results 3.1. Reports of aggressive incidents During the study period of 1 year, 27% (n = 14) of all participants were reported to be aggressive. According to SOAS-R registrations, these 14 participants were responsible for a total of 74 aggressive incidents. Of the whole study sample, 73% (n = 37) did not display aggression, 14% (n = 7) caused one incident, 10% (n = 5) caused from 2 to 10 incidents and 4% (n = 2) caused at least 11 incidents. 3.2. Differences between individuals who displayed aggression and individuals who do not Individuals who displayed aggression (i.e. participants with one or more SOAS-R registration form) and individuals who did not (i.e. participants without SOAS-R registrations) did not significantly differ on sex (x2 = 0.6, p = .44), age (t(49) = 1.49, p = .14) and intelligence (t(48) = .25, p = .80). The three diagnostic groups were equally represented in the aggressive as well as in the non-aggressive group. Demographics of both groups are presented in Table 1. In Table 2, the aggressive and non-aggressive group are compared on cognitive shifting (measured by neuropsychological tasks and rating scales), severity of ASD-symptoms and externalising problem behaviour. Not surprisingly, individuals who displayed aggression were rated significantly higher on externalising problem behaviour than individuals who did not

Table 2 Mean, standard deviation and range of the scores on study measures, for aggressive and non-aggressive individuals. n Task-based composite score of shifting Non-aggressive Aggressive WCST Non-aggressive Aggressive CANTAB ID/ED Non-aggressive Aggressive Rating-based composite score of shifting Non-aggressive Aggressive BFRS-R Non-aggressive Aggressive BRIEF shifting Non-aggressive Aggressive ABL Non-aggressive Aggressive ABCL externalising Non-aggressive Aggressive

37 14

M

SD 0.01 0.03

0.87 0.75

Range 1.38 to 3.01 1.11 to 0.93

37 14

90.9 97.1

44.4 51.8

8–144 19–144

37 14

116.9 105.1

57.1 36.3

61–369 69–163

37 14

0.16* 0.42*

0.95 0.80 10.0 8.0

2.04 to 1.67 0.84 to 1.43

37 14

17.0 21.7

37 14

15.9* 18.6*

4.0 3.4

8–23 13–24

37 14

11.7 13.4

8.7 7.0

0–31 1–24

37 14

17.0** 33.3**

12.3 13.8

0–40 6–33

1–57 14–58

Note. Task-based composite score of shifting = composite score of WCST and CANTAB ID/ED scores; WCST = Wisconsin Card Sorting Test, total number of trials; CANTAB ID/ED = Cambridge Neuropsychological Test Automated Battery, Intra Dimensional/Extra Dimensional Task, total number of trials; Ratingbased composite score of shifting = composite score of BFRS-R and BRIEF scores; BFRS-R = Behaviour Flexibility Rating Scale-Revised, total score; BRIEF shifting = Behaviour Rating Inventory of Executive Function, total score on domain shifting; ABL = Checklist severity of autistic symptoms, total score; ABCL externalising = Adult Behaviour Checklist, total score on domain externalising. * p  0.05; **p  0.01

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Table 3 Provocations of aggressive incidents in percentages. Provocation

%*

Unclear Other client(s) Request to client Being denied something Unexpected situations Bad news Change of activity Help with ADL Other

5.4 9.5 41.9 40.5 12.2 2.7 2.7 1.4 8.1

*

More than one provocation could be marked in each domain of the SOAS-R, so the total percentage could exceed 100%.

(t(49) = 4.09, p  .01, r = .50). More strikingly, but in line with Visser et al. (Submitted), the groups did significant differ in shifting impairment as measured by the BRIEF (t(49) = 2.20, p  .05, r = .30) and the rating-based composite score of BRIEF and BFRS-R ratings (t(49) = 2.01, p  .05, r = .28), but not in severity of ASD-symptoms (t(49) = .63, p = .54). No significant differences were found on neuropsychological task performance (t(49) = .168, p = .87). The task-based composite score and the rating-based composite score of shifting were not significantly correlated (r = .05, p = .75, n = 51). The correlation between the two neuropsychological tasks (r = .38, p  .01, n = 51) as well as the correlation between the two ratings scales (r = .77, p  .01, n = 51) was significant. 3.3. Provocations of aggression The reported provoking factors for aggressive incidents in our study sample are outlined in Table 3. Situations in which the participant had to perform a requested task or in which the participant was denied something were the most provocative ones, accounting for approximately 80% of all aggressive incidents. The distribution of provocations was comparable for the three diagnostic groups. 3.4. Differences between diagnostic groups (ID, ID + ASD, ASD) The three diagnostic groups were examined in additional analyses to aid the interpretation of our main findings. The groups did not significantly differ in sex (x2 = 1.4, p = .49) and age (F(2, 48) = 2.74, p = .08). As a result of our inclusion procedure, the ASD-group had significant higher intelligence as measured by GIT Form Board (M = 13.1) than the ID-group (M = 7.2) and the ID + ASD-group (M = 9.2, F(2, 47) = 16.5, p  .01, r = .64). Also, severity of ASD-symptoms was significantly different for the three diagnostic groups (F(2, 48) = 23.8, p  .01, r = .71). Post hoc pairwise comparisons using Fisher’s least-significance difference indicated that ASD symptoms severity scores in ASD-group (M = 20.4) were higher than in the two ID-groups, and that the ID + ASD-group (M = 12.7) had higher ASD symptom severity scores than the ID-group (M = 6.1). Shifting was similar across the three diagnostic groups on most shifting measures, apart from the BRIEF: significantly more shifting impairment was reported on the BRIEF in the ASD-group (M = 17.9) and the ID + ASD-group (M = 17.6) compared to the ID-group (M = 14.9, F(2, 48) = 3.5, p  .05, r = .35). Neuropsychological test outcome and ratings of externalising problem behaviour did not significantly differ between the three diagnostic groups. 4. Discussion 4.1. Shifting impairment, severity of ASD and aggression The primary aim of this study was to compare impairment in shifting and severity of ASD symptoms in individuals who did and individuals who did not display aggression according to staff registrations. Participants who displayed aggression had significant more impairment in rated shifting than participants who did not. No significant difference between the groups was found on severity of ASD symptoms. This is in line with results of a previous study, in which rated shifting scores, unlike severity of ASD-symptoms, were found to be associated with ratings of externalising problem behaviour (Visser et al., Submitted). Our results support the findings of Kanne and Mazurek (2011) that ASD symptom severity as assessed by clinicians is not associated with aggression. Consequently, the high prevalence rates of aggression that have been reported in ASD (Lerner et al., 2012; Mazurek, Kanne, & Wodka, 2013) and in ID + ASD (Brosnan & Healy, 2011; McClintock et al., 2003) can not directly be explained through ASD symptoms but instead may be linked to impairment in shifting.

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For clinical practice this means that we should concentrate more on the role of shifting when analysing aggression, instead of explaining aggression in terms of ID and ASD diagnoses and their corresponding symptoms. This is in agreement with the multiple deficits model of ASD, in which ASD is depicted as a collection of separate characteristics and core cognitive impairments which have distinct causes (Happe´ & Ronald, 2008). The multiple deficits model of ASD opposes the global assumption that the triad of core impairments in ASD (impairments in social interaction, communication deficits, restricted/repetitive behaviours and interests) is a unitary concept that stems from a single cause (Happe´ & Ronald, 2008; Pellicano, 2011). Though the core symptoms may coexist above chance, they are independent from each other and can also be found in isolation. The cognitive heterogeneity that has been reported in ASD (Geurts et al., 2009; Gonzalez-Gadea et al., 2013) is consistent with the multiple deficits model: cognitive symptoms may be present in some, but not all individuals with ASD. Indeed, not all individuals with ASD experience shifting difficulties. We did find scores on shifting impairment to be higher in the two ASD-groups than in the ID-group without ASD, but only on the BRIEF shifting scale. Neither the neuropsychological tasks nor the BFRS-R and the rating-based composite score of shifting gained significance. The scarcity of significant differences on shifting impairment between those with and those without ASD underscores the value of using a cognition-based approach instead of a diagnose-based approach when examining aggression: those individuals who display shifting impairment are prone to display aggression, regardless of their diagnoses. The statement above needs to be accompanied by some critical remarks. Firstly, the relation between impairment in rated shifting and aggression is not one on one: not all participants who displayed aggression had high scores on shifting impairment and not all participants with high scores on shifting impairment did indeed display aggression. For those without high shifting impairment scores, other identified risk markers may have acted as underlying factors for aggression, such as severity of ID (McClintock et al., 2003; McTiernan, Leader, Healy, & Mannion, 2011) or limitations in communication and social skills (Mazurek et al., 2013; McClintock et al., 2003). Conversely, some characteristics or skills of non-aggressive individuals may have compensated for their shifting deficits. For example, higher IQ scores and intact social skills may serve as ‘protecting’ factors in the relationship between shifting impairment and aggression. A second remark concerns the fact that we found significant differences between the aggressive and the nonaggressive group only on rated shifting and not on neuropsychological tasks of shifting. Neuropsychological task performance and ratings of shifting impairment were not found to be significantly correlated, confirming earlier conclusions that these two measures might assess different constructs (Mahone et al., 2002; Teunisse et al., 2012; Vriezen & Pigott, 2002). In the literature, there is an ongoing debate about the ecological value of neuropsychological executive functioning tests, in which the laboratory test setting is considered as being overstructured and lacking the demands of ‘the real world’ (for a review, see Kenworthy et al., 2008). Neuropsychological tasks are indeed generally designed to measure specific constructs and aim at a high construct validity, where rating scales are more targeted at ecological validity (Chaytor & Schmitter-Edgecombe, 2003). It is a challenge to design measures that have both high construct and ecological validity: increasing ecological validity always comes at the cost of reducing the mechanistic purity of the task (Geurts et al., 2009). The focus on measuring narrow constructs could explain the absence of a correlation between neuropsychological tasks and the broader concept of aggression, for the tasks do not capture possible elements that might influence whether shifting deficits result in aggression. Rating scales on the other hand, may not measure ‘pure’ cognitive shifting, but might be more capable of measuring shifting within the complexity of environmental factors that affect individuals in everyday life. 4.2. Provocations of aggression The secondary aim of this study was to explore provocations that lead to aggression in individuals with ID and ASD. The most reported provocative situations were those in which the participant had to perform a requested task or in which the participant was denied something. These provocations were reported in 80% of all aggressive incidents. Our data are not directly comparable with studies on incidence and provocations of aggression in other care settings, because we have used the SOAS-R version that has been developed for residential care for individuals with ID (Nijman, 2005). This version is relatively new and has more answer options for scoring provocative antecedents of aggression than the original SOAS-R that has been used in former studies (12 and 6 answer options, respectively). Nevertheless, the patient being denied something has also been reported as the most provocative situation in studies on aggression in the elderly (37.9%; Almvik, Rasmussen, & Woods, 2006), in psychiatric patients (44.4%; Grassi, Peron, Marangoni, Zanchi, & Vanni, 2001) and in individuals with mild ID (48%; Tenneij & Koot, 2008). Unfortunately, it was not possible to relate provocations of aggression to shifting impairment in this study. While each participant was scored only once on shifting, several registrations could be filled in for one participant, and several provocations could be scored per registration. Also, it turned out to be difficult to accurately differentiate between the listed provocations: e.g. item ‘hearing bad news’ may show overlap with item ‘unexpected situation(s)’ and item ‘asked to perform a requested task’ could be the reason for item ‘change in activity’. It would be valuable to develop a modified aggressionregistration instrument in which provocations of aggression are more sharply outlined and can easily be related to cognitive functions such as shifting. This instrument could be used in future research to examine if there is a relation between antecedents of aggressive incidents and impairment in shifting, so that it can be elucidated why these antecedents of aggression are so provocative.

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4.3. Limitations with suggestions for future research The current study has some potential limitations and underlies suggestions for future research. First of all, study results should be interpreted taking into account that our sample size was relatively small. Replication with a larger sample is warranted to determine the generalizability of our results. A second concern may be the potential overlap in response items between different rating scales. The rating-based composite score is a combination of BFRS-R and BRIEF shifting scores. BRIEF shifting response items are descriptions of behaviour as a response to situations that require shifting (e.g. ‘bothered by having to deal with changes’ and ‘trouble changing from one activity to another’). One may therefore argue that the BRIEF measures the same construct as the ABCL: i.e. problem behaviour. However, the ABCL response items describe problem behaviour without mentioning the antecedents of this behaviour, where the BRIEF shifting items specifically describe behaviours as a result of shifting impairment. In addition, the other component of the rating-based shifting score (the BFRS-R) does not contain behavioural responses. The BRIEF shifting was found to be significantly correlated to the BFRS-R. Thus, we can be confident that the rating-based composite score has indeed measured shifting impairment and not problem behaviour. Thirdly, though aggression has been noted as a major problem in residential care, the amount of registrations of aggressive incidents that were received during the research period of 1 year was not remarkably high: 74 incidents by 14 out of 51 participants. In line with other studies, we found a minority of the participants who displayed aggression to be responsible for the majority of aggressive incidents (Abderhalden et al., 2007; Almvik et al., 2006; Grassi et al., 2001; Ketelsen, Zechert, Driessen, & Schulz, 2007; Tenneij & Koot, 2008). Possibly, less aggressive incidents were reported than actually took place during the research period. Several studies have addressed the problem of underreporting (e.g. Abderhalden et al., 2007; Nijman et al., 2005; Tenneij, Goedhard, Stolker, Nijman, & Koot, 2009). It has been proposed that a decrease of reported aggressive incidents in SOAS-R assessments over time could be due to a learning effect: because the SOAS-R requires professional carers to systemize observations of their clients, they might become more competent to recognize and adequately manipulate provocations of aggression (Nijman et al., 2005). Abderhalden et al. (2007) compared SOAS-R registrations of psychiatric patients with daily staff reports and found only mild incidents to be underreported, with an estimated underreporting of 30%. In a similar type of study, Tenneij, Didden, et al. (2009) and Tenneij, Goedhard, et al. (2009) concluded that underreporting is likely to occur with the SOAS-R, which makes the instrument less suitable to measure the absolute number of aggressive incidents. However, with daily reports data as a reference, they found that after one month of data collection 81% of the clients were correctly classified into aggressive and non-aggressive subgroups with the SOAS-R. Correct classification improved to 88% when the data collection period was extended to three months. A kappa value of .75 indicated good agreement between both methods of categorization (Tenneij, Didden, et al., 2009; Tenneij, Goedhard, et al., 2009). This evidence suggests that we can be confident that administration of the SOAS-R during 12 months has resulted in representative aggressive and non-aggressive groups in the present study. 5. Conclusions Despite limitations, the current study offers a new insight to the problem of aggression in individuals with ASD, with and without ID. Whether they are diagnosed with ID, ASD or both: individuals who display aggression face more shifting difficulties than non-aggressive individuals. Possibly, aggression will effectively reduce for those individuals with shifting deficits when interventions are aimed at reducing shifting impairment. A change in focus from ID and ASD diagnoses to cognitive shifting requires a well-established cognition-based model for aggression. In order to realize this model, it is important to identify and analyse factors that influence the relationship between shifting and aggression. For example, hierarchical multiple regression procedures could be used to analyse possible moderator and/or mediator effects of intelligence, sex, age, social intelligence and social competence (Frazier, Tix, & Barron, 2004). Furthermore, in-depth interviews with professional cares may provide insights into which and how client-linked factors interact in evoking aggressive outbursts. We will apply both methods in future research. Conflict of interest statement The authors state no conflict of interest in the current study. Acknowledgements This research was supported by the Consortium ‘Stronger on your own feet: Prevention of functional disabilities and decline in adults with intellectual disabilities’, a collaborative association between the Radboud University Medical Centre Nijmegen and three Dutch service providers for people with intellectual disabilities: Dichterbij, Pluryn and Siza. The authors would like to thank these service providers along with two service providers for individuals with ASD; Yulius Autisme, de Steiger and Dr. Leo Kannerhuis, for their collaboration in this study. Also, we wish to express our gratitude to all participating clients who underwent neuropsychological testing and their family, professional carers and psychologists who completed questionnaires and rating scales, for their kind cooperation. Furthermore, a special thanks goes out to Jeroen Oudshoorn for collecting the data used in this study.

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