Attributional and emotional determinants of aggression in people with mild intellectual disabilities

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Attributional and emotionaldeterminants of aggression in peoplewith mild intellectual disabilitiesWarren Bakera & Paul Bramstona

a University of Southern QueenslandPublished online: 22 Jan 2014.

To cite this article: Warren Baker & Paul Bramston (1997) Attributional and emotional determinantsof aggression in people with mild intellectual disabilities, Journal of Intellectual and DevelopmentalDisability, 22:3, 169-185

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Journal of Intellectual & Developmental Disabitit-); Vol. 22, No. 3, pp. 169-185, 1997

Attributional and emotional determinants of aggression in people with mild intellectual

disabilities 1

WARREN BAKER

PAUL BRAMSTON

University o f Southern Queensland

This study investigated links between anger, hostility, and aggressive behaviour in people with mild intellectual disabilities. The study aimed to determine (a) whether relationships between anger, hostility, and aggressive behaviour in a sample of people with mild intellectual disabilities were similar to those found in the general population, and (b) whether hostility was linked to aggressive behaviour by the mediating influence of anger. One hundred and three participants responded to the State-Trait Anger Expression Inventory (Spielberger, 1988), the Cook and Medley (1954) Hostility Scale, the Aggression Question- naire (Buss & Perry, 1992), and the Minnesota Multiphasic Personality Invento- ry, Lie Scale (Hathaway & McKinley, 1951). Results suggest that the effect of hostility on aggression is mediated by anger. An implication of these findings is that people with mild intellectual disabilities may benefit from training programs aimed at the cognitive and affective components of aggression.

Factors implicated in the aetiology of human aggression range from genetics, neuro- anatomy, endocrinology, and physiology through to emotions, cognitions, and envi- ronmental influences (Huesmann, 1994). No one factor, however, is able to fully explain the cause of aggressive behaviour, much less predict who will engage in such behaviour (Eron, 1982). Whilst much research has been conducted among the general population, few studies address the determinants of aggression in people with mild intellectual disabilities.

Aggression

Aggression is often accompanied by strong negative emotional states such as anger. Furthermore, Geen (1990) suggests that the emotional state of anger is most often

~Address for correspondence: Warren Baker, Psychology Department, The University of Southern Queensland, Toowoomba Qld 4350 Australia

1326-978X/97/030169-17 © 1997 Australian Society for the Study of Intellectual Disability Inc.

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170 Baker & Bramston

thought of as a mediating condition that instigates, then guides aggressive behaviour. Rothenberg (1981) asserts that anger may serve as a triggering mechanism for the expression of aggressive behaviour. Klaczynski and Cummings (1989) lent support to Rothenberg when they found that aggressive boys reported greater aggressiveness towards a hypothetical peer, following exposure to laboratory simulations of both prosocial and angry interactions between adults, than did non-aggressive boys.

Huesmann and Eron (1989) argue that aggression can also be represented internally as a collection of specific "scripts" for social behaviour (emphasising aggressive responding). They further argue that aggressive persons (a) enact these scripts, (b) alter evaluative processes to make aggression more acceptable, and (c) both store new aggressive scripts and reinforce older ones, resulting in a set of cognitive structures that promote consistent forms of aggression over time and across situations.

The measurement of aggressive behaviour has been accomplished by using instruments such as the Buss Durkee Hostility Inventory - BDHI (Buss & Durkee, 1957). Buss and Perry (1992) contend, however, that scales on the BDHI were established a priori, with no factor analysis of items. Accordingly, they constructed a new self- report instrument, the Aggression Questionnaire, to meet current psychometric stand- ards. When constructing the Aggression Questionnaire, Buss and Perry obtained significant correlations between self-reported anger, hostility, physical aggression, and verbal aggression in a sample of adolescents. In order to measure and anger, hostility, and aggression in more detail, and to determine whether similar results to those of Buss and Perry could be obtained using different measures, anger was measured by the Trait-Anger Scale of the State-Trait Anger Expression Inventory, Research Edition (Spielberger, 1988) hostility was measured by the Cook and Medley Hostility Scale (Cook & Medley, 1954), and the Physical Aggression and Verbal Aggression subscales of the Aggression Questionnaire were used as a subjective measure of aggression.

Anger

Anger is the emotion most commonly associated with aggressive behaviour and was therefore included in this study. Novaco (1978) suggests that individuals who are chronically angry develop maladaptive styles that predispose them to view events as more frequently and intensely provoking. Lopez and Thurman (1986) support Nova- co's (1978) contention. They found that among college students, aversive events, cognitive appraisals of events, and behavioural reactions to these events were significantly associated with the experience of anger. Beck (1976) similarly recognised anger as an emotion distinct from aggressive behaviour. He suggested that the strength of the angry response is determined by such intellectual or cognitive factors as value judgements, self-esteem, and expectations.

Selby (1984) provided empirical support for the notion that assessment of anger may be useful in discriminating aggressive from non-aggressive individuals. He found that the Novaco Anger Inventory (Novaco, 1975) correctly classified 88% of violent and 92% of non-violent incarcerated criminals. Similarly, Unverzagt and Schill (1989) report that the Trait-Anger Scale of the State-Trait Anger Inventory (Spielberger,

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Attribution and emotional determinants o f aggression 171

1988) accurately classified 69% of aggressive college students. Whilst previously mentioned studies suggest that the Novaco Anger Inventory may be a more valid measure of anger, the language used in scale items was considered too complex to be properly understood by people with mild intellectual disabilities. The Trait-Anger Scale was used to measure anger in the present study.

Cognitive factors also appear to be involved in the expression of aggression. More specifically, research evidence suggests that angry, aggressive individuals may need to possess hostile beliefs, concerning antecedent cues and consequences, before they will express aggressive behaviour (Allred & Smith, 1993; Bargh, 1982; Dodge & Coie, 1987; Dodge & Frame, 1982; Dodge, Murphy, & Buchsbaum, 1984; Dodge & Tomlin, 1987; Epps & Kendall, 1995).

Hostility

Hostility has been described as an attitudinal variable reflecting the tendency to view others as motivated by selfish concerns, as likely sources of provocation and mistreat- ment, and as generally untrustworthy (Smith & Christensen, 1992). Social information-processing theory (Dodge, 1980; Dodge, Pettit, McClaskey, & Brown, 1986) proposes that the tendency to make hostile-biased attributions leads an individual to display angry, reactive-aggressive behaviours (but not necessarily instrumentally aggressive behaviours). Research also suggests that hostile attributional biases make it more likely that the behaviour of others will be interpreted as antagonistic or threatening (Dodge & Coie, 1987; Dodge & Frame, 1982).

Hostile attribution bias It has been previously noted that hostile persons apparently maintain a "hostile other schema", which potentially influences perceptions of others and the processing of related social information (see Dodge & Cole, 1987; Dodge & Frame, 1982). Indeed, research has found that aggressive individuals in the general population are more likely than non-aggressive individuals to recall only hostile cues in a stimulus array, to be vulnerable to recency effects, and to mislabel prosocial intentions as hostile (Allred & Smith, 1993; Bargh, 1982; Epps & Kendall, 1995: Dodge et al., 1984; Dodge & Tomlin, 1987). Self-reported hostility has also been found to be associated with a greater frequency of angry and suspicious thoughts, as well as the tendency to interpret the actions of others as intentionally provocative (Pope, Smith, & Rhodewalt, 1990; Smith, Sanders, & Alexander, 1990).

Whilst hostility is certainly not synonymous with overt aggression, most views suggest that hostile persons are more likely to display aggressive behaviour (Smith et al., 1990; Spielberger et at., 1985). The Cook and Medley Hostility Scale (Cook & Medley, 1954) was used as a self-report measure of hostility in the present study.

Aggression, anger, and hostility Having examined aggression, anger, and hostility individually, the interaction of these three concepts will now be considered. Previous research appears to indicate that individuals who have deveioped a 'bad attitude' towards others (hostility) are more

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likely to get angry and to act out their angry hostile thoughts more frequently (aggression). Although previously reviewed research (e.g., Dodge et al., 1984; Dodge & Tomlin, 1987) focuses on this implicit attribution-behaviour linkage, the mediating processes that occur in this thought-to-action sequence have yet to be fully investigated.

Graham, Hudley, and Williams (1992) provide support for a thought, emotion, action sequence in the development of aggression. Furthermore, their analyses support the mediational role of anger in the development of aggressive behaviour, with both aggressive and non-aggressive adolescents. Figure 1 graphically depicts this thought, emotion, behaviour sequence. Graham et a/.(1992), however, developed their model on the general population. This study is the first exploratory attempt to replicate this model among people with mild intellectual disabilities.

HOSTILITY ANGER

AGGRESSION

Figure 1. An attribution-emotion sequence of aggression

Aggression and intellectual disability For the purposes of this study, intellectual disability refers to "significantly sub- average intellectual functioning resulting in or associated with a concurrent impairment in adaptive behaviour" (Strongman, 1985, p. 202). Within this definition intellectual functioning is further defined as that which is assessed by general intelligence tests. Significantly sub-average is defined as an Intelligence Quotient (IQ) of 69 or below and impairment in adaptive behaviour is defined as limitations assessed by standardised scales. A person with mild intellectual disabilities is defined as someone who has a full scale IQ between 55 and 69 on either the Wechsler Intelligence Scale for Children - Revised (Wechster, 1974) or the Wechsler Adult Intelligence Scale - Revised (Wechsler, 1981), and is experiencing difficulties in meeting age-appropriate expectations in everyday life.

Tonge and Einfeld (1991) contend that aggressive behaviour is disproportionately prevalent in the intellectually disabled population. Benson and Reiss (1984) also suggest that people with intellectual disabilities are at risk of a wide range of emotional disorders, as well as aggressive behaviour and lack of impulse control. Although the

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Attribution and emotional determinants of aggression 173

figures vary somewhat, :research suggests that between 15 and 30% of people with intellectual disabilities suffer from emotional/behavioural disorders.

Historically, researchers have debated whether people with intellectual disabilities are capable of self-report. Reasons for this debate revolve around difficulties in obtaining reliable and valid responses to questionnaires. Studies (e.g., Sigelman, Budd, Spanhel, & Schoenrock, 1981a; Sigelman, Budd, Spanhel, & Schoenrock, 1981b; Sigelman et al., 1980; Zetlin, Herriot, & Turner, 1985) document evidence of acquiescence (i.e., a tendency to agree with the nature of the content of a statement) and social desirability (i.e., a bias or set to respond to self-evaluative questions in a socially approved of manner so as to try to please or appear more socially desirable either to themselves or to others). Research also suggests that various language and communication skills decrease with lower IQ levels (Keane, 1972; Sigelman & Werder, 1975; Spradlin, 1963). Due to deficient cognitive, verbal, and social skills, people with intellectual disabilities may be especially prone to response biases (Heal & Sigelman, 1995).

Despite these difficulties, several studies provide evidence of seemingly reliable and valid data from people with mild intellectual disabilities (e.g., Bramston, Bostock, & Tehan, 1993; Kabzems, 1985; Miller, Voelker, & Shaw, 1987). Research using slightly modified self-report measures and information obtained from caters/supervi- sors also provides evidence of response consistency (e.g., Benson & Ivins, 1992; Lindsay & Luckason, 1991).

Methodology of the present study

The current study utilised a semi-structured interview format. Structure and memory load problems were minimised by presenting short, closed questions dealing with concrete issues. To facilitate the interview format, the wording of scale items was altered to correspond with the idiom of people with mild intellectual disability. Visual aids also accompanied all item choices. Because self-report scales consisted of forced choice (true/false) and Likert scale type questions, the Minnesota Multiphasic Person- ality Inventory, Lie Scale (Hathaway & McKinley, 1951) was administered to all subjects to control for acquiescence and response bias. Probe questions were also used by the interviewer to confirm understanding and seek further information. It should be noted, however, that all of the instruments used in this study were designed and tested on American college students, probably of above intellectual ability. Therefore, the reliability, validity, and other psychometric properties of these instruments cannot simply be assumed to apply to people with mild intellectual disabilities.

The current study grew out of concern for the lack of understanding of people with mild intellectual disabilities exhibiting aggressive behaviour. Furthermore, the appar- ent futility of only treating their aggressive behaviour led to the inclusion of emotion (anger) and cognition (hostility). If the three-part model, linking hostility to aggression through the mediating influence of anger is validated, it is anticipated that better staff/parent/self training, and more appropriate intervention programs will follow.

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METHOD

Participants

Questionnaires were administered to 108 people with mild intellectual disabilities (male, n = 76; female, n = 32). In order to identify individuals who were trying to please or who may be responding in a socially approved manner, participants completed the Lie Scale from the Minnesota Multiphasic Personality Inventory (Hathaway & McKinley, 1951). Five participants with Lie Scale scores of 8 or above were found and inspection of their responses suggested that they were intentionally lying or responding in a socially approved of manner. Their responses were therefore excluded from the study. The final sample contained 103 participants (male = 73; female = 30).

Participants were special school students (n = 31) and employees of sheltered workshops (n = 72) situated in both urban and rural areas of South East Queensland. Ages ranged from 12 to 61 years. The mean age was 27 years with a standard deviation of 12.30. All participants resided in supported community housing or with their families.

Participants were selected on the following criteria: (a) individuals had been previously assessed as functioning in the mild range of intellectual disability (based on agency files, ie., IQ between 55-69 on the WAIS-R, WISC-R); (b) they exhibited sufficient verbal skill to enable them to take part in a simple conversation (based on staff reports); (c) they were not suffering from any other disorder (based on agency files, e.g., dementing disorder, depression etc.); and (d) they volunteered to participate in the project. Categorisation of participants by age, gender, and type of facility is presented in Appendix A. For younger participants, parental consent was obtained. Participants were assured of confidentiality.

Measures

Participants responded to four instruments: the Trait-Anger Scale (T-Anger) of the State-Trait Anger Expression Inventory, Research Edition (Spielberger, 1988), the Cook and Medley Hostility Scale (Cook & Medley, 1954), the Physical and Verbal Aggression subscales of the Aggression Questionnaire (Buss & Perry, 1992), and the Minnesota Multiphasic Personality Inventory, Lie Scale (Hathaway & McKinley, 1951).

All of the above instruments, however, were designed and tested on non-intellectually disabled college students. Therefore, the psychometric properties of these instruments cannot simply be assumed when they are used in a population of people with intellectual disabilities. Further psychometric problems are also introduced by the strategy of rewriting and modifying components of a number of the questionnaires, to make them more intelligible to people with intellectual disabilities. These modified instruments should be regarded as new instruments which require trials to establish their reliability, validity, and psychometric properties. It should also be noted that no normative data exists for people with intellectual disabilities for any of the measures used in this study. All reliability and validity coefficients quoted in this section refer to

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the non-intellectually disabled population.

State-Trait Anger Expression Inventory, Research Edition (STAXI) The T-Anger scale comprises 10 items which measure individual differences in the disposition to experience anger. Scores potentially range from 10 to 40, with high scores indicating a higher disposition to experience anger. Subjects rate themselves on a 4-point scale, where 1 = almost never; 2 = sometimes; 3 = often; 4 = almost always. Test-retest reliability appears substantial with an alpha coefficient of .87 being reported (Spielberger, 1988). The wording of the items was altered to facilitate the interview format. For example the statement, "2 am quick tempered" was replaced with, "Are you quick tempered?".

Cook & Medley Hostility Scale (Ho) This scale comprises 50 items derived from the Minnesota Multiphasic Personality Inventory (Hathaway & McKinley, 1951) and identifies individuals characterised by a dislike for, and distrust of, others. Participants respond to items as being either true or false and scores potentially range from 0 to 50, with high scores indicating higher levels of hostility. Internal consistency appears acceptable, with Contrada and Jussim (1992) reporting an alpha coefficient of .83. The original scale was also language simplified because of the language complexity of 37 of the items. For example, the statement, "Most people are honest chiefly through the fear of being caught", was replaced with "Most people are honest because they are scared of being caught".

The Aggression Questionnaire (AQ) The physical and verbal aggression subscales of the AQ were used to measure direct/ overt and indirect aggression.

The Physical Aggression Scale (PA) is a 9-item subscale which measures overt (physical) aggression. Subjects rate themselves on a 5-point scale, where 1 = not at all; 2 = a little; 3 = a fair bit; 4 = a lot; 5 = always. Scores potentially range from 9 to 45. High scores indicate higher levels of physical aggression.

The Verbal Aggression Scale (VA) is a 5-item subscale which measures indirect (verbal) aggression. Scores potentially range from 5 to 25, with high scores indicating high levels of verbal aggression. The internal consistency of this scale appears adequate, with alpha coefficients of .85 (PA) and .72 (VA) being reported (Buss & Perry, 1992). Test-retest correlations over a 9-week interval, of .80 (PA) and .76 (VA) suggest stability over time (Buss & Perry, 1992).

To facilitate the interview format, 14 scale items were altered. For example, the statement, "Once in a while I can't control the urge to strike another person", was replaced with, "Once in while you can't control the feeling that you want to hit someone".

Lie Scale (L) The L scale is designed to identify individuals deliberately responding in a socially approved manner and comprises 15 items relating to attitudes and practices that are socially undesirable, but common. Subjects respond to items as being either true or

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false. Scores potentially range from 0 to 15. Greene (1980) contends that scores of 8 or above are suggestive of a purposeful socially desirable response.

The L scale appears internally consistent, with alpha coefficients from .60 to .72 being reported (Robinson, Shaver, & Wrightsman, ! 991). Test-retest correlations for intervals of up to one week range from .70 to .85 (Greene, 1980). Evidence for concurrent validity is available from studies showing high correlations with similar constructs, for example, Eysenck's Lie Scale, r = .83,p < .01, (Paulhus, 1986) and the Marlow-Crowne scale, r = .81, p < .01 (Edwards & Walsh, 1964).

The scale was designed for use among the general population and it was necessary to make some minor adjustments to the wording in order to use it with people with mild intellectual disabilities. For example, Item 4 (I do not read every editorial in the newspaper each day) and item 14 (Sometimes at elections I vote for men about whom I know very little), were considered inappropriate for the test sample. Item 4 was replaced with, "No-one cares much what happens to me", whilst item 14 was replaced with, "I sometimes feel that I am about to go to pieces". Replacement items originate from the MMPI and form part of the Edwards Social Desirability Scale (Edwards, 1957). All 15 items were language simplified. For example, the statement, " I gossip a little at times", was replaced with, "Sometimes you tell tales about others".

PROCEDURE

Modification of test measures Despite widespread usage of all the selected scales in the general population, problems relating to complexity of language and the suitability of items for people with mild intellectual disabilities were envisaged. Prior to testing, a panel consisting of two special school teachers and three individuals currently working with people with intellectual disabilities examined the wording of all test instruments. Panellists were requested to propose questionnaire modifications that would facilitate subjects' comprehension of test items. Panellists were also requested not to alter item content or sentence length if possible. Where possible, synonyms were identified which were readily understood by people with or without intellectual disabilities. Modified scales were analysed via the Flesch Index (Flesch, 1948) to quantitatively gauge ease of comprehension. A visual aid (a series of buckets - empty through to full) accompanied the numeric choice to facilitate comprehension for those who were not accustomed to using Likert scales.

Upon completion of modification, and prior to commencement of testing, scales were administered in a trial to a sample of five people with mild intellectual disabilities to ascertain unforeseen difficulties. Qualitative observations suggested that subjects' responses to all scales were adequate. No difficulties were experienced with scale wording or the interview format.

Interview format Test instruments were administered verbally in the form of a semi-structured interview. Interviews were conducted over a two month period at the participants' school

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or place of employment. Participants were interviewed on an individual basis by the researcher with each interview taking approximately 40 minutes. All test measures, including subscales, were presented in a counterbalanced order. In order to monitor comprehension, the majority of subjects' responses were verified with the prompt: "Tell me more about that." Any items not understood or unable to be answered were noted.

RESULTS

Descriptive statistics

The means and standard deviations for males, females, and the total sample on each of the 5 scales are presented in Table 1.

Table 1

Means, standard deviations, and range for males, females, and the total sample

Male Female Total Sample (n = 73) (n = 30) (n = 103)

M SD SD M D D Range

6.46 19.87 5.53 21.23 6.24 11-33 7.74 28.67 9.25 29.67 8.19 11-49 7.25 18.50 7.48 21.04 7.47 10-38 3.14 10.63 3.48 11.17 3.24 6-20 1.38 4.40 1.59 4.39 1.44 1 -7

Anger 21.79 Hostility 30.08 PA 22.08 VA 11.38 Lie 4.38

Note. VA = Verbal Aggression, PA = Physical Aggression, L = Lie Scale. For all scales high scores indicate high levels of a particular construct.

Analyses were carried out to determine whether there were any gender and age differences. Age cut-off points of 12 to 18 years for adolescents, and 19 years and above tbr adults, were used. One way analysis of variance revealed a significant difference between mean scores for males and females on the measure of Physical Aggression, F(1,101) = 5.09, p < .05. No significant differences were found for Anger, Hostility, or Verbal Aggression. Results indicate that males in this sample report higher levels of Physical Aggression than do females.

Significant differences were also found between adolescent and adult mean scores for Anger, F(1,101) = 16.98, p < .001, Hostility, F (1,101) = 17.37,p < .001, Physical Aggression, F (1,101) = 34.56, p < .001, and Verbal Aggression, F(1,101) = 5.79, p < .05. Results indicate that adolescents in this sample experience higher levels of Anger, Hostility, and Aggression than do adults.

T-tests revealed no significant differences between the mean Lie Scale score for the total sample and mean scores reported in other studies (e.g., Hathaway & McKinley, 1951; Swenson, Pearson, & Osbourne, 1973). As such, Lie Scale scores may provide some evidence for the reliability and validity of subjects' responses.

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Correlational analyses

A correlational analysis was conducted, to examine the relationships between anger, hostility, physical aggression, and verbal aggression. A summary of the Pearson product-moment coefficients for the total sample is presented in Table 2.

As expected, all variables were significantly intercorrelated. Positive correlations for self-report measures of anger, hostility, physical aggression, and verbal aggression were moderate to high. Results suggest that individuals with high scores for physical and verbal aggression also experience high levels of anger and hostility.

Table 2

Pearson product-moment coefficients for all measures

Variable Anger Host PA VA

Hostility .64** PA .80** .61"* VA .62** .56** .68**

Note. N=103. P A = Phys ica l Aggress ion , V A = Verbal Aggress ion. * p <.01. ** p <.001. All tests two-tai led.

Partial correlation analysis

Having established that there were significant correlations between hostility, anger, and aggression, the data were examined for relationships directly between hostility and aggression without the anger component, which the literature suggested is a mediator between the two. In order to do this, a partial correlation analysis was conducted, with anger controlled. The outcome is presented in Table 3.

Table 3

Partial correlation coefficients controlling for anger

Variable Hostility PA VA

PA .22* VA .27** .40***

Note. N = 103. P A = Phys ica l aggression, V A = Verbal aggression. * p < .05. **p < .01. ***p < .001. All tests two-tailed.

With anger controlled, the correlations between hostility and both physical and verbal aggression were substantially lower. This suggests that much of the relationship between hostility and aggression can be explained by their shared variance with anger. Without anger, the relationship between hostility and aggression is considerably weaker.

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Predicting aggressive behaviour

In order to test whether both physical and verbal aggression can be predicted by self- reported hostility and anger, a stepwise multiple regression was performed, with hostility and anger as the independent variables and a combined measure of physical and verbal aggression as the dependent variable. A multiple R of .82 was obtained, accounting for 67% (66% adjusted) of the variance, F(2,100) = 99.61, p < .001. Both hostility and anger clearly made significant contributions to the prediction of aggression in people with mild intellectual disabilities.

In order to determine whether hostility contributed to the prediction of anger, a stepwise multiple regression was performed, with hostility as the independent variable and anger as the dependent variable. A multiple R of .64 was obtained, accounting for 41% (40% adjusted) of the variance, F(1,101) = 70.32, p < .001. This indicates that hostility contributed significantly to the prediction of anger. The unstandardised regression coefficients (B), the standardised regression coefficients (B), and the standard error (SE B) for both of the above regression analyses are presented in Tables 4 and 5, respectively.

Table 4

Summary of regression analysis for anger and hostility predicting aggression

Variable B SE B B

Anger 1.05 .12 .65** Hostility .27 .09 .22*

Note. N=I03. R2=.67. *p<.01. **p<.001.

Table 5

Summary of regression analysis for hostility predicting anger

Variable B SE B B

Anger .49 .06 .64**

Note, N= 103. R2= .41. **p<.001.

Proposed model

In order to establish a framework or model which reflects the relationships found between hostility, anger, and aggression, the three-part causative model proposed within the introduction was tested.

In the model depicted in Figure 2, hostility (cognition) is thought to affect anger (emotion) and aggression (behaviour) directly (signified by arrows). In addition hostility affects aggression indirectly, as mediated by anger. The total effect of hostility on aggression is the sum of its direct effect, and its indirect effect, through anger. Anger has only a direct effect on aggression in this model.

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HOSTILITY ANGER .65

AGGRESSION

Figure 2. Path diagram for the mediated model of aggression

The path coefficients indicating the direct effects of hostility and anger on aggression are .22 and .65, respectively. Using these coefficients, which were obtained from the preceding regression analyses, the direct effect of anger on aggression may be interpreted as approximately three times as large as that of hostility alone on aggression. It should be noted that the path coefficients are represented by standardised beta values.

The indirect effect of hostility on aggression (i.e., as mediated by auger) may be obtained by multiplying the effect of hostility on anger by the effect of anger on aggression (Pedhazur & Schmelkin, 1991). The indirect effect of hostility on aggression is (.64)(.65) = .42. Using these coefficients, the indirect effect of hostility on aggression may be interpreted as approximately twice as large as the direct effect (i.e., .22) of hostility on aggression. The total effect of hostility on aggression is .22 + .42 = .64. Results indicate that the mediated effect of hostility on aggression is stronger than the direct effect. Overall, results appear to support a model where hostility is linked to aggression through the mediating influence of anger. Caution, however, should be exercised when interpreting these results, as the untested reliability of the modified measures and the high correlations obtained may have affected the magni- tude and stability of the regression coefficients.

DISCUSSION

The present study investigates a cognitive attributional approach to aggression that also incorporates emotion. The relationships found between hostile attitudes, angry emotions, and aggressive behaviour in this sample of people with mild intellectual disabilities appear consistent with previous studies of these constructs in the general population (e.g., Buss & Perry, 1992; Graham et al., 1992). Furthermore, the correlations suggest, that as with individuals without disabilities, people in this study who are chronically aggressive and angry appear to have hostile attitudes or personalities that predispose them to view events as more frequently and intensely provoking (see Pope et al, 1990; Smith et al., 1990).

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Buss and Perry (1992), suggest that the correlations between hostility and both physical and verbal aggression may in part be due to their connection with anger. The results of this study support this theory. People with hostile attitudes who are more readily prone to angry emotions are more likely to be aggressive.

The three-part model linking hostility to aggression through the mediating influence of anger was therefore validated and extended to include a new population, those with mild intellectual disabilities. As in the general population, aggression in this sector of the community appears to occur because of an escalating sequence of hostile antagonistic thoughts, angry emotions, and behavioural responses. This thinking, feeling, action sequence also appears consistent with Graham et al.'s (1992) study of aggressive behaviour in non-intellectually disabled adolescents.

Age and gender differences

Although no predictions were made regarding age or gender differences it was found that adolescents self-reported higher levels of anger, hostility, and aggression on all measures. Results also indicate that males in this study are more physically aggressive than females. There were no gender differences for anger, hostility, and verbal aggression. One way of integrating these findings is to suggest that whilst aggressive males experience similar levels of anger, hostility, and verbal aggression to females, they might not have learned appropriate ways of expressing their angry, hostile feelings.

Intervention implications

Many psychological interventions that focus on aggression, both in the general population and in people with intellectual disabilities traditionally depend upon a behavioural focus. For example, aggressive individuals with or without mild intellectual disabilities are typically punished for aggressive behaviour or rewarded for non- aggressive behaviour. The focus is on the aggressive behaviour, and feelings of anger or hostile thoughts mad attributions are often forgotten.

More recent research on aggression in the non-intellectually disabled population, however, has shown an increasing interest in the development of intervention programs for aggressive individuals based on social cognitive skill training (e.g., Coie & Koeppl, 1990). Furthermore, some empirically-based programs that include a cognitive component have shown promising results (e.g., Guerra & Slaby, 1990). This trend is consistent with the results of this study which suggest that interventions could be focused on the aggressive behaviour, the angry emotions, the hostile attitudes, or all three simultaneously. The tentative relationships found in this study between hostility, anger, and aggression suggest that aggressive people with mild intellectual disabilities may also benefit from participation in programs addressing not only the behavioural but also the cognitive and affective components of aggression. The results have important implications for the development of multifocused aggression management programs, particularly when conceptualised in terms of a thinking, feeling, acting sequence. It seems reasonable to suggest that an appropriate starting point for

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intervention would be training aggression-prone people how to perceive the intent of others. According to the model feelings of anger should then be diminished. An important implication for practitioners might not so much be management of anger reduction, as training individuals to realise that anger can be an appropriate emotional response when negative actions of other are clearly guided by hostile intent.

Reliability and validity of data

A number of factors indicate that data obtained in this study are reliable. The interview technique appeared to facilitate participants' comprehension of scale items. From a qualitative viewpoint, prompts and requests for details appeared to be an effective mechanism for preventing response set and acquiescence. Quantitative measures also support the reliability of the data, in that mean Lie Scale scores fell within the normative range for the non-intellectually disabled population.

Limitations and methodological considerations

Whilst encouraged by the present findings, a number of methodological considerations need to be raised. It should be recognised that the phenomenon being studied is complex, involving the interplay of negative life events, individual characteristics, and coping behaviottrs. The design used is limited in view of this complexity. The study is also limited by a lack of standardised instruments for assessing anger, hostility, and aggression in people with intellectual disabilities. The findings must therefore be regarded as purely preliminary and require further replication. Finally, caution must be exercised when drawing implications from the findings due to the study's exploratory nature and the psychometric problems encountered in modifying scales. Nonetheless, the value of the study as a model for intervention, based on attributional change, should not be understated.

Future research

The current study highlights the need for further research into the nature and precipi- tants of aggression in people with mild intellectual disabilities. Future research should be directed at expanding the model tested in this study to determine whether cognitive appraisal acts as a mediator between hostile attributions and emotional responses. The modified instruments used in this study should be regarded as new instruments. As such, further research should be conducted to establish their reliability, validity, and other psychometric properties. It is also recommended that this study be replicated with other populations, such as children or prisoners.

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APPENDIX A

Age, gender, and facility of participants

Age Special Schools Sheltered Workshops Males Females Males Females (n = 26) (n = 5) (n = 46) (n =26)

10-18 26 5 3 1 19-29 17 9 30-39 15 8 40-49 6 5 50-59 5 3 60-69 1

Note. N= 103. The mean age for males is 26.21; the mean age for females is 29.20. A total of 193 (Special Schools = 58; Sheltered Workshops = 135), people with mild intellectual disabilities were identified as potential participants.

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Attributional and emotional determinants of aggression in people with mild intellectual disabilities