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. Author manuscript; available in PMC: 2022 May 1.
Published in final edited form as: J Autism Dev Disord. 2021 May;51(5):1496–1507. doi: 10.1007/s10803-020-04627-9

Assessing Irritability in Children with Autism Spectrum Disorder Using the Affective Reactivity Index

Carla B Kalvin 1, Theresa R Gladstone 1, Rebecca Jordan 1, Sonia Rowley 1, Carolyn L Marsh 1, Karim Ibrahim 1, Denis G Sukhodolsky 1
PMCID: PMC7855357  NIHMSID: NIHMS1616736  PMID: 32734421

Abstract

Irritability is an impairing problem in children with ASD that may be associated with other behavioral and emotional concerns. The Affective Reactivity Index (ARI) is a parent-rated measure of irritability widely used in children with mood disorders, however, its utility in children with ASD remains unclear. In this study, we examined ARI parent ratings in children with ASD and contributions of parent-rated anxiety and noncompliance to irritability measured by the ARI. Participants included 81 children with ASD, aged 8 to 16 years. Results suggest that both anxiety and noncompliance contribute to irritability, but that anxiety only contributes to irritability in the absence of noncompliance. Further, the ARI is likely to be a useful measure of irritability in children with ASD.

Keywords: autism spectrum disorder, irritability, anxiety, noncompliance

Irritability is a concerning and common problem among children with autism spectrum disorder (ASD). Historically, irritability has been widely studied in children with ASD, although the term irritability has often encompassed a broader category of behavior problems, including aggression, temper tantrums, and self-injury (Fung et al., 2016). Defined in this way, irritability has been the focus of dozens of clinical trials, including the seminal work by the Research Units on Pediatric Psychopharmacology (RUPP) Autism Network on the use of the atypical antipsychotic, risperidone, in the treatment of irritability in children with ASD (Aman et al., 2009; McCracken et al., 2002). In these clinical trials, irritability has been operationally defined using the 15-item Irritability scale of the Aberrant Behavior Checklist (ABC) (Aman & Singh, 2017; Aman, Singh, Stewart, & Field, 1985; Farmer & Aman, 2020). Despite the widespread use of the ABC Irritability scale (ABC-I) in ASD samples, including as the primary outcome measure in important clinical trials, the ABC was originally developed for individuals with intellectual and developmental disabilities. Recent psychometric analyses indicate that the ABC-I items reflect a wider range of behavioral manifestations of irritability, such as self-harm, relative to manifestations of the mood component, such as feeling angry (Kaat, Lecavalier, & Aman, 2014; Stoddard, Zik, Mazefsky, DeChant, & Gabriels, in press). As a result, the affective element of irritability may not be as well captured by the ABC-I.

More recently, a conceptualization of pediatric irritability has emerged that places a greater emphasis on affective phenomena. Defined as a reduced threshold for experiencing anger that arises from frustration (Brotman, Kircanski, & Leibenluft, 2017), irritability is conceptualized as related to but distinct from disruptive behaviors such as aggression, which is a potential, but not necessary, manifestation of irritable mood. Within the DSM-5 diagnostic classification, irritability is a core symptom of disruptive mood dysregulation disorder (DMDD) and oppositional defiant disorder (ODD) and a common symptom of depression and anxiety disorders (American Psychiatric Association, 2013). As a dimensional category, pediatric irritability has been indexed by the 7-item measure called the Affective Reactivity Index (Stringaris et al., 2012). While the Affective Reactivity Index has been widely used to examine irritability in children with mood and disruptive behavior disorders, little is known about its utility in children on the autism spectrum. Thus, the primary aim of this study was to characterize the emotional component of irritability in children with ASD using the parent-rated Affective Reactivity Index (ARI). We also examined the association of affective irritability with the core symptoms of ASD, as well as with co-occurring symptoms of anxiety and noncompliance.

Recent studies indicate that high levels of affective irritability are common in children with ASD. Using the 2-item Disruptive Mood Dysregulation subscale of the Pediatric Behavior Scale (Lindgren & Koeppl, 1987), Mayes and colleagues found that 43% of children with ASD had elevated levels of irritability (Mayes et al., 2019). In addition to the risk factors for irritability that can be common across childhood disorders, irritability in children with ASD may also arise due to challenges conferred by the core symptoms of the disorder. For example, difficulty communicating one’s thoughts, feelings or needs to others, having one’s repetitive behaviors prevented or interrupted, and exposure to aversive sensory experiences may result in frustration and heightened irritability (Kanne & Mazurek, 2011; Mazefsky, Day, & Golt, 2019). In addition, interpersonal and social communication difficulties that place children with ASD at risk for negative social experiences, such as peer rejection, may engender feelings of hostility and anger (Mazefsky et al., 2019). In children with ASD, irritability and disruptive behaviors are likely to persist over time (Shattuck et al., 2007; Simonoff et al., 2013) and contribute to functional impairment over and above the unique effects of ASD (Storch et al., 2012). Irritability and disruptive behavior also pose significant disruption to family life, resulting in heightened parental stress and interference in daily functioning for families of children with ASD (Lecavalier, Leone, & Wiltz, 2006; Storch et al., 2012).

Irritability also cuts across a wide range of psychiatric disorders and often exists in conjunction with emotional and behavioral disturbances that commonly co-occur with ASD. Anxiety, for instance, which occurs in up to 40% of children with ASD (Lecavalier et al., 2019), may be associated with irritable mood and temper outbursts common in ASD. Indeed, elevated levels of anxiety and irritability have been found among children with high-functioning ASD (Mayes, Calhoun, Murray, Ahuja, & Smith, 2011), and anxiety has been positively associated with irritability in young children and adolescents on the autism spectrum (Mikita et al., 2015; Sukhodolsky et al., 2019). The association between these two sets of symptoms may reflect a pattern by which the experience of anxiety leads to elevated irritability (Tantam, 2003). For example, anxiety-inducing events (e.g., a social performance situation) may engender irritability or exacerbate existing irritable mood. The association between anxiety and irritability may be particularly relevant for children with ASD, for whom difficulties with emotional awareness and communication may increase frustration in response to negatively valanced emotions.

Noncompliant behavior, another problem common among children with ASD (Baker & Blacher, 2015; Lecavalier et al., 2019), is also likely to be associated with symptoms of irritability. In children, noncompliance occurs in response to limits or demands imposed by parents or other authority figures and when such limits are perceived as interfering with a child’s desires or goals (e.g., parental requests regarding bedtime conflict with child’s desire to stay awake and play video games). Such real or perceived blocked goals, in turn, can lead to frustration and thereby elevate risk for irritability. Supporting this link, in children without ASD, noncompliance has been associated with irritability (Axelson et al., 2012). In children with ASD, noncompliant behavior may specifically function as a way to gain access to restricted and repetitive behaviors and activities. Further, since restrictive behavior and rigidity, including insistence on sameness and difficulty with transitions, may predispose children with ASD to experience daily parental limits as challenging, noncompliance in children with ASD may be especially associated with frustration and increased susceptibility to irritability. While few studies have examined the co-occurrence of noncompliance and affective irritability in ASD, a recent study by Mayes and colleagues of 580 children with ASD supports the association between these two sets of symptoms (Mayes et al., 2015). In this study, 93% of children with ASD and clinically significant noncompliant behavior, measured using the oppositional behavior scale of the Pediatric Behavior Scale (Lindgren & Koeppl, 1987) (n = 296), were reported as having irritable mood often or very often, and 82.4% were reported as having temper outbursts often or very often. In contrast, of children with ASD without clinically significant noncompliant behavior (n = 284), 30.6% and 19.7% were reported as having irritable mood and temper outbursts, respectively. Another study examining noncompliance in 124 children and adolescents with ASD showed a significant association between irritability, measured with the ABC-I, and noncompliance, measured with the Home Situations Questionnaire (r = .29) (Chowdhury et al., 2010).

Given the prevalence of irritability among children with ASD, as well as the fact that irritability is likely to be associated with other emotional and behavioral problems that often co-occur with ASD, we examined the associations of irritability with anxiety and noncompliance in a well-characterized sample of children with ASD. Irritability was measured by the parent-rated Affective Reactivity Index, a measure that has become widely used in children with mood disorders without ASD and that may provide a useful tool for measuring the affective aspect of irritability in children on the autism spectrum. The Affective Reactivity Index (ARI) (Stringaris et al., 2012) is a 7-item measure of irritability, operationalized as a reduced threshold for experiencing angry mood (see Methods section for details). In children and adolescents without ASD, the ARI has demonstrated excellent psychometric properties (Mulraney, Melvin, & Tonge, 2014; Stringaris et al., 2012). However, only two studies have used the ARI to measure irritability in children with ASD. In their study comparing 47 boys with ASD, 40 boys with severe mood dysregulation, and 23 boys without ASD or mood disturbances, Mikita and colleagues used the ARI to measure irritability (Mikita et al., 2015). Boys with ASD showed irritability levels that were higher than boys without ASD or mood disturbances and comparable to boys with severe mood dysregulation. Leno and colleagues used the ARI in a study of 43 adolescents with ASD to examine associations of irritability with perceptual processing (Leno et al., 2018). Thus, despite the potential value of the ARI as a measure of irritability in children with ASD, little is known about its utility in this population. Further, no studies have investigated how the ARI functions as a measure of irritability that may co-occur with other emotional and behavioral difficulties comorbid with ASD.

In the present study, our first aim was to examine parent ratings on the ARI, including the internal consistency and distribution of item-responses, in children with ASD with and without co-occurring anxiety and disruptive behavior disorders. Using these ratings of irritability, our second aim was to examine the associations of irritability with anxiety and noncompliance, as well as the unique and combined contributions of anxiety and noncompliance to irritability. We predicted that irritability would be positively associated with anxiety and noncompliance but that there would be a stronger association between irritability and noncompliance than between irritability and anxiety. We also predicted that there would be an interactive effect of anxiety and noncompliance whereby the effect of anxiety on irritability would be stronger for children with higher levels of noncompliance.

Methods

Participants

Participants included 81 children with ASD (aged 8 to 16 years) who were recruited from a university autism program and participated in studies of neuroimaging or behavior therapy. Diagnosis of ASD was based on the ADOS-2 and ADI-R, administered by clinicians trained to research reliability and confirmed by the expert clinician. Co-occurring disorders were assessed by a structured clinical interview, and the principal co-occurring diagnosis was assigned based on the chief co-occurring concern warranting the family’s visit to the autism program. Of these children, 42 had a principal co-occurring anxiety disorder (ASD+anxiety), 18 had a principal co-occurring disruptive behavior disorder (ASD+DBD), and 21 had ASD without co-occurring anxiety or disruptive behaviors (ASD-only). Participant demographic and clinical characteristic data are shown in Table 1.

Table 1.

Participant Demographics and Clinical Characteristics

ASD+anxiety (n=42) ASD+DBD (n=18) ASD-only (n=21) p value
Age, Mean (SD) 12.15 (1.75) 12.65 (2.06) 12.53 (2.19) .59
Full Scale IQ, Mean (SD) 99.81 (19.71) 103.39 (16.52) 102.95 (20.05) .73
ARI Total Irritability, Mean (SD) 4.31 (3.38) 9.17 (2.07) 1.29 (1.31) <.001abcd
MASC-2 Total Anxiety, Mean (SD) 70.69 (13.74) 62.56 (15.41) 50.00 (7.96) <.001acd
HSQ Noncompliance, Mean (SD) 2.15 (1.21) 3.35 (1.43) 0.65 (0.66) <.001abcd
ADOS-2, Mean (SD)
 SA 10.69 (3.69) 12.06 (3.21) 9.81 (3.89) .16
 RRB 2.26 (1.71) 3.83 (1.25) 3.00 (1.95) <.01ab
 Total 12.95 (4.37) 15.89 (3.61) 12.81 (4.68) .04ab
ADI-R, Mean (SD)
 A 22.05 (5.33) 19.67 (5.51) 18.57 (4.56) .03ad
 B 16.74 (4.61) 16.06 (3.70) 14.95 (4.07) .30
 C 7.33 (2.39) 7.56 (2.43) 4.29 (2.55) <.001abd
Sex, Number (%) .43
 Male 31 (73.8) 16 (88.9) 16 (76.2)
Race, Number (%) .72
 Asian 3 (7.1) 1 (5.6) 0 (0.0)
 Black or African American 1 (2.4) 1 (5.6) 0 (0.0)
 White 34 (81.0) 14 (77.8) 20 (95.2)
 More than one race 4 (9.5) 2 (11.1) 1 (4.8)
Ethnicity, Number (%) .10
 Hispanic or Latino 9 (21.4) 1 (5.6) 1 (4.8)
 Not Hispanic or Latino 33 (78.6) 17 (94.4) 20 (95.2)
DSM-5 diagnoses, Number (%)
 Anxiety disorder 42 (100.00) 10 (55.6) 0 (0) <.001
  Generalized anxiety disorder 25 (59.5) 1 (5.6) 0 (0) <.001
  Social anxiety disorder 24 (57.1) 0 (0.0) 0 (0) <.001
  Specific phobia 13 (31.0) 8 (44.4) 0 (0) <.001
  Separation anxiety 5 (11.9) 1 (5.6) 0 (0) .10
 Obsessive compulsive disorder 5 (11.9) 0 (0.0) 1 (4.8) .56
 Oppositional defiant disorder 6 (14.3) 16 (88.9) 0 (0) <.001
 Attention-deficit/hyperactivity disorder 21 (50.0) 14 (77.8) 7 (33.3) .02
 Depressive disorder 4 (9.5) 0 (0.0) 0 (0.0) .14
 Trichotillomania 2 (4.8) 1 (5.6) 0 (0.0) .57
Taking psychiatric medication, Number (%) <.01
 Stimulants 7 (16.7) 6 (33.3) 2 (9.5) .15
 Alpha Agonists 7 (16.7) 5 (27.8) 2 (9.5) .32
 Antidepressants 6 (14.3) 6 (33.3) 2 (9.5) .11
 Neuroleptics 3 (7.1) 5 (27.8) 0 (0) .01
 Mood Stabilizers 0 (0.0) 3 (16.7) 0 (0) <.01
 Benzodiazepines 1 (2.4) 2 (11.1) 0 (0) .15
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Note. ASD+anxiety = ASD and comorbid anxiety; ASD+DBD = ASD with disruptive behaviors; ASD- only = ASD without comorbid anxiety or disruptive behaviors. ARI = Affective Reactivity Index. MASC- 2 = Multidimensional Anxiety Scale for Children, 2nd edition. HSQ = Home Situations Questionnaire. ADOS-2 = Autism Diagnostic Observation Schedule-2nd edition. ADOS-2: SA- Social affect; RRB- Restricted and repetitive behavior. ADI-R = Autism Diagnostic Interview-Revised. ADI-R: A- Qualitative abnormalities in reciprocal social interaction; B- Qualitative abnormalities in communication; C- Restricted, repetitive, and stereotyped patterns of behavior. Full-scale IQ measured by the Differential Ability Scales-II or the Wechsler Abbreviated Scale of Intelligence.

a

Significant group differences at p <.05, with Bonferonni correction

b

ASD+DBD > ASD+anxiety

c

ASD+DBD > ASD−only

d

ASD+anxiety > ASD−only

e

ASD+anxiety > ASD+DBD

Procedures

The diagnosis of ASD was made based on the Autism Diagnostic Observation Schedule, 2nd edition (ADOS-2) (Lord et al., 2012) and the Autism Diagnostic Interview-Revised (ADI-R) (Le Couteur, Lord, & Rutter, 2003), which were administered by a research-reliable clinician. Co-occurring psychiatric disorders were assessed using the Anxiety Disorders Interview Schedule for Children and Parents (ADIS-C/P) (Silverman & Albano, 1996) or the Schedule for Affective Disorders and Schizophrenia for School-Age Children- Present and Lifetime Version (K-SADS-PL) (Kaufman et al., 2016), and both were administered by an expert clinician. The Differential Ability Scales-II (DAS-II) (Elliott, 2007) or the Wechsler Abbreviated Scale of Intelligence (WASI) (Wechsler, 1999) was used to measure Full Scale IQ. Children in the study had Full Scale IQ scores ranging from 67 to 141 (mean = 101.42, SD = 18.99). Parents of all children provided demographic information and medical history, and they completed questionnaires regarding children’s symptoms of irritability, noncompliance, and anxiety.

Study procedures were approved by the university Institutional Review Board. Prior to data collection, parents provided written informed consent and children provided assent. For children who participated in clinical trials of behavior therapy, this study reports baseline data (i.e., data collected prior to study intervention).

Measures

The Affective Reactivity Index (ARI) (Stringaris et al., 2012) is a 7-item scale that assesses children’s irritability symptoms over the past six months. In this study, the parent-rated version of the ARI was used. Items on the ARI are rated on a 3-point scale ranging from 0 (not true) to 2 (certainly true). The first six items measure symptoms of irritability (e.g., “is easily annoyed by others,” “gets angry frequently”) and are used to compute the total irritability score. Total scores of 3 or higher are considered clinically significant. The seventh item, not included in the total score, assesses impairment due to irritability. Higher scores on the ARI reflect higher levels of irritability. The ARI has demonstrated good internal consistency in children with ASD (α = .82) (Mikita et al., 2015) and showed excellent internal consistency in the current sample (α = .90).

The Home Situations Questionnaire (HSQ) is a parent-rated 25-item scale that assesses child noncompliance with parental instructions, rules or commands (Chowdhury et al., 2010). The 25-item version of the HSQ was adapted for children with ASD by the Research Units on Pediatric Psychopharmacology (RUPP) Autism Network from the original version of the HSQ, designed to measure noncompliance in children without ASD. Each item on the HSQ corresponds to a different situation (e.g., “at mealtimes,” “when asked to do homework”), and the parent indicates if his or her child has demonstrated noncompliance in that situation over the past week. For each situation endorsed, the parent rates the severity of the noncompliance on a 9-point scale ranging from 1 (mild) to 9 (severe). The sum of severity scores across all items is divided by 25 to obtain the HSQ mean severity score, with higher scores reflecting higher levels of child noncompliance. The 25-item adapted version of the HSQ has good internal consistency in children with ASD (α = .80 – .90) (Chowdhury et al., 2010) and demonstrated excellent internal consistency in the current sample (α = .92).

The Multidimensional Anxiety Scale for Children, 2nd edition (MASC-2) (March, 2012) is a 50-item scale used to measure anxiety symptoms in children. In this study, the parent-rated version of the MASC-2 was used. Items on the MASC-2 are rated on a 4-point scale ranging from 0 (never) to 3 (often) and used to compute the Total Anxiety scale. Higher scores on the Total Anxiety scale reflect greater anxiety symptomatology. The parent-rated version of the MASC-2 shows excellent internal consistency for children with ASD, both in previous studies (α = .92) (Kaat & Lecavalier, 2015) and in the current study (α = .93).

The ADOS-2 (Lord et al., 2012) and ADI-R (Le Couteur et al., 2003) were also used as indexes of ASD symptom severity. The ADOS-2 is a clinician-administered observational assessment that combines unstructured conversation, structured activities and interview questions to evaluate ASD symptomatology and diagnose ASD. All ADOS-2 administrations in this study were conducted with Module 3, appropriate for verbally fluent children. The ADOS-2 Module 3 algorithm yields subscale scores in the domains of Social Affect (SA) and Restricted and Repetitive Behavior (RRB), in addition to a Total Score, which can be used establish classification as autism, autism spectrum, or non-spectrum. Higher scores on the ADOS-2 reflect greater ASD symptom severity.

The ADI-R is a clinician-administered semi-structured interview conducted with the child’s caregiver and used to assist with diagnosis of ASD. The items on the ADI-R are scored based on the caregiver’s responses to questions about the child’s current and lifetime functioning. The ADI-R algorithm yields total scores in the following areas: Qualitative Abnormalities in Reciprocal Social Interaction, Qualitative Abnormalities in Communication, and Restricted, Repetitive, and Stereotyped Patterns of Behavior (RRB). Higher scores on the ADI-R reflect greater ASD symptom severity.

Data Analyses

Data analyses were conducted using SPSS v24 (IBM corp. 2017). To examine group differences in demographic and clinical characteristics, one-way analysis of variance (ANOVA) and chi square tests were conducted using Bonferroni adjustments to correct for multiple comparisons. To examine the associations of irritability with anxiety and noncompliance, as well as with demographic and clinical characteristics, we conducted zero-order correlations between ARI irritability, MASC-2 anxiety, HSQ noncompliance, age, gender, IQ, and ASD symptom severity variables (measured by the ADOS-2 and ADI-R) using Pearson correlations. To compare the association between irritability and anxiety with the association between irritability and noncompliance, the Fisher r-to-z transformation was used. Next, to examine the contributions of anxiety and noncompliance to irritability, a hierarchical linear regression predicting ARI irritability was conducted. Controlling for age, gender and IQ, the unique, combined, and interactive effects of anxiety and noncompliance on irritability were examined. For all of the correlational and regression analyses, the total sample combined across the three diagnostic groups (N = 81) was used. We also report descriptive statistics for the ARI items and the distribution of the total ARI score to illustrate the utility of this measure in children with ASD.

Results

Demographic and clinical characteristics of the sample are reported in Table 1. Among the three diagnostic groups, there were no significant differences in age, gender, race, ethnicity, or IQ. However, among the three groups, there were significant differences in anxiety, with higher scores in the ASD+anxiety and ASD+DBD groups compared to the ASD-only group, and in noncompliance and irritability, with highest scores in the ASD+DBD group, followed by the ASD+anxiety group, followed by the ASD-only group. There were also significant differences in ASD symptom severity, with greater deficits in ADI-R reciprocal social interaction in the ASD+anxiety group compared to the ASD-only group, higher levels of ADI-R RRBs in the ASD+anxiety and ASD+DBD groups compared to the ASD-only group, and higher levels of ADOS RRBs and overall ADOS symptom severity in the ASD+DBD group compared to the ASD+anxiety group.

ARI total irritability scores ranged from 0 to 12 (mean = 4.60, SD = 3.85). As seen in Figure 1, scores were skewed towards the low end of the scale, with scores of 0 and 1 corresponding to 16.0% and 18.5%, respectively, of the sample. Sixty one percent of the sample had scores greater than or equal to 3, falling in the clinically significant range. ARI scores differed significantly among the three diagnostic groups (p < .001), with highest scores in the ASD+DBD group (mean = 9.17, SD = 2.07), followed by the ASD+anxiety group (mean = 4.31, SD = 3.38), followed by the ASD-only group (mean = 1.29, SD = 1.31). The internal consistency of the ARI was excellent, Cronbach’s alpha = .90.

Figure 1.

Figure 1.

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Distribution of Affective Reactivity Index total irritability score in the total sample (N = 81).

Table 2 reports the means and standard deviations for each of the six ARI items that comprise the total irritability score, the percentage of the sample with scores of 1 (“somewhat true”) or 2 (“certainly true”) on each item, and the correlation of each item with the total irritability score. The item most frequently rated as 1 or 2 was “is easily annoyed by others,” (endorsed by 70.5 % of the sample) followed by “often loses his/her temper” and “loses temper easily” (each endorsed by 60.3% of the sample). The least frequently endorsed item was “is angry most of the time,” with only 24% of the sample having ratings of 1 or 2 on this item. All six items showed strong correlations with the total irritability score (r range = .70 – .92), with “gets angry frequently” and “loses temper easily” demonstrating the highest correlations with ARI total irritability.

Table 2.

Affective Reactivity Index Item Analysis for the Total Sample (N =81)

ARI Item Mean SD n (% somewhat true or certainly true) Item total correlation
Is easily annoyed by others 1.01 .78 70.5 .70**
Often loses his/her temper .95 .87 60.3 .89**
Stays angry for a long time .60 .84 37.2 .81**
Is angry most of the time .28 .53 24.4 .73**
Gets angry frequently .76 .79 53.8 .90**
Loses temper easily .92 .85 60.3 .92**
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Note. ARI = Affective Reactivity Index.

**

p < .01

Age, gender and IQ were not associated with irritability, anxiety, or noncompliance. Of the six ASD symptom severity variables, only ADI-R RRB was associated with irritability, anxiety, and noncompliance (rs = .38, .30, and .42, respectively; ps < .01). Irritability was positively associated with anxiety (r =.30, p < .01) and positively associated with noncompliance (r =.67, p < .001). However, the association between irritability and noncompliance was significantly larger than the association between irritability and anxiety (z = −3.13, p < .01). Anxiety and noncompliance were also positively associated (r =.35, p < .01). See Online Resource 1 for the full table of correlations.

The hierarchical linear regression predicting irritability was conducted in three steps. To control for heterogeneity conferred by age, gender, and IQ, these variables were entered in the first step. To examine the unique and combined contributions of anxiety and noncompliance to irritability, anxiety and noncompliance were entered in the second step. Lastly, to examine potential interactive effects, the interaction between anxiety and noncompliance was entered in the third step. The results of these analyses are presented in Table 3. After accounting for age, gender, and IQ, anxiety and noncompliance, entered as a block, accounted for 46% of the variance in irritability, p < .001. However, when included together in this step, there was a unique contribution of noncompliance (β = .63, p < .001), but not anxiety (β = .12, p = .18). When tested in the third step, the interaction between anxiety and noncompliance was significant (β = −1.08, p = .01). This interaction is graphically depicted in Figure 2. For children with low levels of noncompliance, higher levels of anxiety contributed to heightened irritability, whereas, for those with high levels of noncompliance, level of anxiety had no effect on irritability. Together, these results signify that while both anxiety and noncompliance contribute to irritability, noncompliance has a larger effect on irritability that is independent of anxiety. Further, the effect of anxiety on irritability is mitigated in the presence of high levels of noncompliance.

Table 3.

Hierarchical Regression Analysis of Irritability as a Function of Anxiety and Noncompliance in the Total Sample (N = 81)

Variable R2 β ΔF
Step 1 .04 1.17
Age .06
Gender .12
IQ .18
Step 2 .50 34.05***
Anxiety .12
Noncompliance .63***
Step 3 .54 6.91*
Anxiety × Noncompliance −1.08*
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Note.

*

p < .05.

***

p < .001.

Figure 2.

Figure 2.

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Irritability as a function of the interaction between anxiety and noncompliance in the total sample (N =81). Noncompliance and anxiety dichotomized using a median split.

Discussion

The present study investigated irritability using the parent-rated Affective Reactivity Index (ARI) in a well-characterized sample of children with ASD. The first aim was to examine internal consistency and characterize the distribution of item-responses on parent ratings on the ARI in children with ASD, including children with and without co-occurring anxiety and disruptive behavior disorders. In this sample, the internal consistency of the ARI was excellent, and ARI scores ranged from 0 to 12, reflecting that the full range of the scale was utilized by the parents when rating their children’s irritable mood. Sixty one percent of the sample fell in the clinically significant range, with total ARI scores greater than or equal to 3. When separated out by diagnostic group formed by the principal co-occurring anxiety or disruptive behavior disorder, children in both the ASD+anxiety and ASD+DBD groups had average scores in the clinically significant range. However, the total ARI scores in the ASD+DBD group were more than double the scores of children in the ASD+anxiety group. In contrast, children in the ASD-only group had much lower scores than children in either of the other groups, and these scores fell below the threshold of clinical significance.

The average level of irritably in the ASD+anxiety and ASD+DBD groups in our sample is consistent with levels of irritability reported in two previous studies that used the ARI in children on the autism spectrum (Leno et al., 2018; Mikita et al., 2015) and similar to the levels of irritability reported in youth with severe mood dysregulation (Stringaris et al., 2012). Together, these results suggest that irritability in some children with ASD is notably elevated, specifically in those with ASD and co-occurring anxiety or disruptive behaviors. Further, among children with ASD and these co-occurring conditions, severity of irritability may be comparable to children with severe mood concerns without ASD.

The relative frequency with which the individual items on the ARI were endorsed in our sample (i.e., “is easily annoyed by others” endorsed most frequently, “is angry most of the time” endorsed least frequently) also parallels the results from the original validation of the ARI in youth without ASD (Stringaris et al., 2012). These results, together with the high internal consistency found for the ARI in the present sample, suggest that the ARI is a useful measure of irritability in children with ASD and that it functions similarly for children with and without ASD.

The second aim of our study was to examine the associations of irritability with anxiety and noncompliance, as well as the unique and combined contributions of anxiety and noncompliance to irritability. As predicted, anxiety and noncompliance were both positively associated with irritability, and the association between noncompliance and irritability was larger than the association between anxiety and irritability. Further, in the regression analysis controlling for age, gender and IQ, anxiety and noncompliance together contributed to irritability, although only noncompliance demonstrated a unique effect.

The link found here between anxiety and irritability parallels prior studies documenting an association between anxiety and irritability in children and adolescents with ASD (Mikita et al., 2015; Sukhodolsky et al., 2019) and is consistent with the notion that anxiety may lead to elevated levels of irritability (Tantam, 2003). In children with ASD, the common experience of anxiety may be especially frustrating in the context of limited emotional awareness and impaired social communication, thus heightening propensity for irritability.

Similarly, our finding of an association between noncompliance and irritability is consistent with research on both children with and without ASD (Axelson et al., 2012; Chowdhury et al., 2010; Mayes et al., 2015). Noncompliance in response to demands imposed by authority figures is most likely to take place in a frustration-inducing context in which the child perceives the demand as a challenge to his or her desires or goals. Restricted and repetitive behaviors central to ASD, such as insistence on performing a behavior in the exact same way each time, are likely to place children with ASD at odds with the demands of home and school environments which require flexibility. As such, for children with ASD, daily demands requiring flexibility (e.g., doing something in a slightly different way, transitioning between activities) may be especially challenging, and thus noncompliance associated with such demands may be particularly associated with increased frustration and irritability.

Further, our findings regarding the relative strength of the associations of anxiety versus noncompliance with irritability, coupled with the unique effect of noncompliance on irritability, suggest that processes related to noncompliance play a larger role in the manifestation of irritability for children with ASD. It may be that anxiety experienced by children with ASD often leads to experiences other than irritability, such as withdrawal and sadness, whereas the experience of blocked goals associated with noncompliance more directly heightens frustration and manifests in irritability.

Regarding the interactive effect of anxiety and noncompliance on irritability, a significant interaction did emerge. However, contrary to our expectations, this interaction reflected a pattern whereby anxiety contributed to irritability only for children with low levels of noncompliance. Although it is plausible that high levels of both anxiety and noncompliance could have a multiplicative effect on irritability, the results here suggest otherwise and indicate that the effect of anxiety on irritability is attenuated in the presence of higher levels of noncompliance. Given the stronger association between noncompliance and irritability, it may be that for children with ASD and high levels of noncompliance, irritability is largely driven by processes surrounding noncompliance (i.e., blocked goals leading to increased frustration) and that additional anxiety does not have a notable impact above and beyond that of noncompliance. In contrast, for children with ASD who have less difficulty with noncompliance, their anxiety may be a more paramount concern impacting their daily lives and thus more readily heighten propensity for irritability.

Clinical Implications

The present findings have relevant implications for clinical practice. Most notably, the results suggest that the ARI is a useful tool for accurately assessing affective irritability in children with ASD and that it may be especially useful in those with co-occurring anxiety and/or disruptive behaviors. The six core items of the ARI map well on to the conceptualization of irritability as a tendency to experience and express anger (e.g., Brotman et al., 2017). As such, using the ARI in children with ASD is likely to specifically capture the affective dimension of irritability in this population. Given the high rates of both behavioral (e.g., physical aggression) and affective (e.g., angry mood) manifestations of irritability in ASD, the use of such a tool is particularly important, especially in cases in which the behavioral manifestations might seem more salient to parents who are reporting on these symptoms. For example, for a child with ASD who frequently engages in physically aggressive behavior, parent’s report of the child’s symptoms may tend to emphasize the physical behavior, which is overt and may be more obviously disruptive to the family. However, given the opportunity to report on the child’s affective state and mood symptoms using the ARI, parents are likely to provide a more complete picture of the child’s affective irritability symptomatology. Alternatively, for a child with ASD and anxiety, and for whom there are not obvious manifestations of aggression, standard clinical assessment practices may neglect assessment of the child’s irritable mood that may be relevant. Use of the ARI, which is short and easy to administer, would provide a practical way to obtain this potentially important clinical information. In these ways, the ARI is likely to be a very helpful tool that provides a convenient and nuanced index of affective irritability, thereby contributing to the comprehensive clinical assessment of children on the autism spectrum, especially for those with co-occurring emotional and behavioral difficulties.

With regard to clinical intervention, our finding that both anxiety and noncompliance contribute to irritability in children with ASD suggests that interventions aimed at reducing irritability in children with ASD may benefit from careful evaluation and, if present, treatment for these co-occurring conditions. To this end, cognitive behavioral therapy for anxiety in children with autism (Wood et al., 2019), and parent training for noncompliance (Bearss et al., 2015) may be helpful in addressing the emotional and behavioral difficulties that heighten risk for irritability in children on the autism spectrum. There is also emerging evidence that cognitive behavioral therapy for anger and aggression (Sukhodolsky & Scahill, 2012) can be adapted for use with children and adolescents on the autism spectrum (Sukhodolsky, Gladstone, Marsh, & Cimino, 2019).

Several limitations of the present study deserve mention. First, the study’s cross-sectional design precludes conclusions regarding the causal nature of the association of anxiety and noncompliance with irritability. Longitudinal studies are needed to examine the links between these constructs over time and test the direction of these associations. Second, the power to detect effects in the current study was limited by the small sample size. Studies with larger samples are warranted for further examining the utility of the ARI in children with ASD and examining how anxiety and noncompliance contribute to irritability in this population. Third, the majority of the participants in this study were seeking clinical services at a specialty autism program in a major research university, so the present results may not be generalizable to non-treatment-seeking populations. Relatedly, the present study sample was comprised of mainly boys, so generalizability of the results to girls on the autism spectrum is unclear. In order to address these limitations, future studies examining the use of the ARI and the influences of anxiety and noncompliance on irritability should be undertaken in epidemiological samples, as well as in samples with a greater proportion of females on the autism spectrum.

Future Research

In addition to the need for studies using longitudinal designs and larger samples, continued research on irritability in ASD is warranted in several other areas. For example, while our study focused on associations of irritability with two of the most frequently co-occurring problems in ASD, anxiety and noncompliance, examining associations with other comorbid conditions, such as Attention Deficit Hyperactivity Disorder (ADHD), is important. ADHD is very common in children with ASD and is highly comorbid with behavioral difficulties, such as noncompliance, in this population (Lecavalier et al., 2019). ADHD is also associated with emotion regulation difficulties that may be related to irritability and anxiety (Shaw et al., 2014; Steinberg & Drabick, 2015). As such, future studies are needed that include large enough groups of children with ASD with and without co-occurring ADHD in order to examine the relative contributions of co-occurring ADHD, noncompliance, and anxiety to irritability in children on the autism spectrum.

Also, while a strength of the present study was the inclusion of children on the autism spectrum both with and without comorbid disorders, research that expands on the current study by further including children with differing diagnostic profiles is needed. Findings from the present study indicate that children with ASD and anxiety or disruptive behavior disorders have clinically elevated levels of irritability, however, the extent to which heightened irritability is associated with these co-occurring conditions versus ASD is unclear. Future studies that include larger samples and additional groups of children with anxiety and/or disruptive behavior disorders without ASD are needed to better dissociate the relative contributions of ASD versus these other forms of psychopathology to irritability. Additionally, studies comparing different subsamples of children (i.e., children with and without ASD and with and without anxiety and/or disruptive behaviors) would allow for examination of how patterns of associations among dimensional measures of irritability, anxiety, and noncompliance, such as those found in the current study, operate among children with differing profiles of ASD and emotional and behavioral difficulties.

Lastly, studies examining neurobiological underpinnings of irritability that compare samples of children with and without ASD and with and without other psychiatric conditions would advance understandings of irritability in ASD. Such studies would allow researchers to examine the extent to which irritability in ASD is associated with neural markers specific to ASD and/or co-occurring conditions, such as anxiety and disruptive behavior (e.g., Ibrahim et al., 2019). Importantly, findings from such studies would help further elucidate mechanisms of irritability in ASD, and specifically, whether these mechanisms qualitatively differ as a function of co-occurring symptomatology.

The present study is the first to investigate how the ARI functions as a measure of irritability that cooccurs with emotional and behavioral difficulties common in children with ASD. Results indicate that the ARI is a useful tool for measuring irritability in children on the autism spectrum, including those with cooccurring anxiety and disruptive behaviors. Findings also suggest that comorbid anxiety and comorbid noncompliance contribute to irritability in this population, however, anxiety only impacts irritability in the absence of noncompliance. Assessing irritability with the ARI is likely to aid in the clinical assessment of children on the autism spectrum and further understandings of emotional difficulties in this population, especially in the presence of noncompliant and disruptive behavior.

Supplementary Material

10803_2020_4627_MOESM1_ESM

Acknowledgements:

This work was supported by National Institute of Mental Health (NIMH) grant R01MH101514 (D.G.S.) and National Institute of Child Health and Human Development (NICHD) grant R01HD083881 (D.G.S.). C.B.K. is a Fellow of the Translational Developmental Neuroscience Training Program (T32 MH18268) directed by Dr. Michael Crowley.

Footnotes

Publisher's Disclaimer: This Author Accepted Manuscript is a PDF file of an unedited peer-reviewed manuscript that has been accepted for publication but has not been copyedited or corrected. The official version of record that is published in the journal is kept up to date and so may therefore differ from this version.

Conflict of Interest: Dr. Sukhodolsky receives royalties from Guilford Press for a treatment manual on CBT for anger and aggression in children. Other authors (C.B.K., T.R.G., R.J., S.R., C.L.M. and K.I.) have no biomedical financial interests or potential conflicts of interest to declare related to this present study.

Ethics Approval and Consent to Participate: This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Yale University School of Medicine Institutional Review Board. Informed consent was obtained from all participants included in the study.

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