868907
research-article2019
AUT0010.1177/1362361319868907AutismHwang et al.
Original Article
Understanding anxiety in adults on
the autism spectrum: An investigation
of its relationship with intolerance of
uncertainty, sensory sensitivities and
repetitive behaviours
Autism
1­–12
© The Author(s) 2019
Article reuse guidelines:
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https://doi.org/10.1177/1362361319868907
DOI:
10.1177/1362361319868907
journals.sagepub.com/home/aut
Ye In (Jane) Hwang1,2 , Samuel Arnold1,2,
Preeyaporn Srasuebkul1 and Julian Trollor1
Abstract
Anxiety is present in high rates in both children and adults on the autism spectrum. An increasing number of studies have
highlighted the potentially important role that intolerance of uncertainty may have in anxiety for those on the spectrum,
as well as their interrelationships with sensory sensitivities and repetitive behaviours. In response to a lack of studies
involving adults, this study examined self-report survey data regarding intolerance of uncertainty, sensory sensitivities,
repetitive behaviours and anxiety in a sample of 176 adults on the autism spectrum (mean age = 42). Intolerance of
uncertainty and anxiety were both found to be elevated relative to non-autistic adults (N = 116) and significant, positive
correlations were found between intolerance of uncertainty, anxiety, repetitive behaviours and sensory sensitivities in
those on the spectrum. Intolerance of uncertainty was found to be a significant mediator between sensory sensitivities
and anxiety, as well as between anxiety and insistence on sameness behaviours. These results were not sensitive to age.
Intolerance of uncertainty is an important factor to be considered in the conceptualisation and management of elevated
rates of anxiety for adults on the autism spectrum.
Keywords
adults, anxiety, intolerance of uncertainty, repetitive behaviours, sensory sensitivities
High rates of anxiety are consistently reported for individuals on the autism spectrum. Recent estimates suggest lifetime rates of anxiety to be between 50% and 65% for
autistic individuals of all ages (Buck et al., 2014; Joshi
et al., 2013; Lever & Geurts, 2016; Lugnegard, Hallerback,
& Gillberg, 2011). In efforts to better understand anxiety
in autism spectrum disorder (ASD), researchers have
examined and conceptualised the involvement of different
underlying mechanisms in the development and maintenance of anxiety in this population.
Most frequently discussed is the role of intolerance of
uncertainty (IU), which is a broad, dispositional factor
characterised by the tendency to react negatively to situations and events that are unforeseen and/or unpredictable
(Buhr & Dugas, 2006). It is found to have strong associations with clinically significant anxiety disorders in the
general population, including generalised anxiety and
social anxiety (Buhr & Dugas, 2006; Carleton, 2012;
Carleton, Norton, & Asmundson, 2007). IU is found to be
elevated in autistic individuals relative to those not on the
spectrum (Boulter, Freeston, South, & Rodgers, 2014;
Maisel et al., 2016; Vasa, Kreiser, Keefer, Singh, &
Mostofsky, 2018). It is significantly associated with anxiety for those on the spectrum and more specifically acts as
a mediator between autism and anxiety in children and
young adults (Boulter et al., 2014; Maisel et al., 2016;
Neil, Olsson, & Pellicano, 2016). Qualitative studies
investigating the experience of anxiety in young autistic
1UNSW Sydney, Australia
2Cooperative Research Centre for Living with Autism (Autism CRC),
Australia
Corresponding author:
Ye In (Jane) Hwang, Department of Developmental Disability
Neuropsychiatry (3DN) and Justice Health Research Program, Kirby
Institute, UNSW Sydney, Wallace Wurth Building, 61-63 Botany St,
Sydney, NSW 2052, Australia.
Email: jane.hwang@unsw.edu.au
2
adults have suggested ideas resonant of IU, such as ‘uncertainty/making decisions’ and ‘unexpected or sudden
change’, to be pertinent sources of anxiety (Trembath,
Germano, Johanson, & Dissanayake, 2012, p. 217).
A number of other factors related to the ASD phenotype
have also appeared in the literature alongside IU and anxiety
in ASD. These include sensory sensitivities and repetitive
behaviours (Boulter et al., 2014; Neil et al., 2016; Wigham,
Rodgers, & South, 2015), which have been alternatively
referred to in literature as ‘sensory processing atypicalities’
and ‘restricted and repetitive behaviours’, respectively
(Rodgers & Ofield, 2018). An emerging body of qualitative
and quantitative studies consistently find interrelationships
between these factors, IU and anxiety in autistic populations
(Black et al., 2017; Gillott & Standen, 2007; Joyce et al.,
2017; Lidstone et al., 2014; Mazurek et al., 2013; Rodgers,
Glod, Connolly, & Mcconachie, 2012; South & Rodgers,
2017; Trembath et al., 2012; Uljarević, Lane, Kelly, &
Leekam, 2016; Wigham et al., 2015).
Sensory sensitivities, both hyper- and hypo-sensitivity,
have primarily been conceptualised as a contributor to
anxiety. Accordingly, one qualitative study of anxiety in
young autistic adults reported ‘sound and light sensitivities’ to be key sources of anxiety (Trembath et al., 2012, p.
217), while quantitative studies find more severe sensory
sensitivities in those with higher anxiety (Gillott &
Standen, 2007; Uljarević et al., 2016). Numerous studies
also report a significant positive association between
repetitive behaviours and anxiety in autistic individuals
(Joyce et al., 2017; Lidstone et al., 2014; Wigham et al.,
2015). Qualitative evidence suggests that repetitive behaviours may be strategies for coping with anxiety and may
also exacerbate anxiety (Joyce et al., 2017).
Based on existing qualitative and quantitative literature
for children and young adults on the autism spectrum,
Figure 1 presents an exploratory framework for the possible pathways involving these variables. This framework is
closely based on the 2017 review by South and Rodgers
(2017) regarding existing literature on the sensory, emotional and cognitive contributions to anxiety in ASD (p. 3).
A number of studies have found evidence for components
of this framework and offered similar models, all involving IU as a mediator of autism characteristics (sensory sensitivities, emotional processing difficulties) and anxiety
(Boulter et al., 2014; Cai, Richdale, Dissanayake, &
Uljarević, 2018; Wigham et al., 2015). Overall, it may be
theorised that sensory sensitivities may exacerbate anxiety
in autistic individuals via an aversion or reaction to uncertainty or unpredictability of the sensory aspects of an event
or situation. Furthermore, repetitive behaviours may be
both a manifestation of, and a coping mechanism for, anxiety, primarily by means of reintroducing certainty, control
or consistency to the anxious situation. This would suggest
that increasing an individual’s tolerance of uncertainty,
which may reduce their anxiety, will likely have effects on
their repetitive behaviours.
Autism 00(0)
Figure 1. Exploratory framework for possible pathways
involving IU in the relationship between anxiety and key autism
features.
IU: intolerance of uncertainty.
While consistent evidence builds in this area, studies
have predominantly focused on children and adolescents and there remains a lack of studies modelling
these relationships in adults. One published study of 76
autistic adults and 75 community comparisons attempted
to model anxiety in autistic adults and its relationship
with IU, alexithymia (difficulty in describing internal
emotional states) and emotional acceptance (Maisel
et al., 2016). This study reported higher rates of IU and
anxiety in autistic adults. No studies have attempted to
model the relationships between IU, anxiety, sensory
sensitivities and repetitive behaviours for adults over
25 years of age.
We also know little about the presentation of these factors in adulthood. A handful of studies report a general
decrease in restricted, repetitive behaviours with age
(Chowdhury, Benson, & Hillier, 2010; Esbensen, Seltzer,
Lam, & Bodfish, 2009; Levy & Perry, 2011). A lack of
evidence exists regarding the developmental trajectory of
sensory sensitivities and IU for autistic individuals, though
both are reported at high rates in adulthood (Crane,
Goddard, & Pring, 2009; Robertson et al., 2018). It will be
important to develop a better framework for understanding
the presentation and interrelationships between these factors in autistic adults, in order to best develop targeted
interventions for anxiety.
This study aimed to examine the relationships between
IU, anxiety, sensory sensitivities and repetitive behaviours (referred to collectively as ‘the study variables’
herein) in autistic adults. Specific aims included the
following:
1.
2.
3.
To compare the levels of the IU, anxiety, sensory
sensitivities and repetitive behaviours between
autistic and non-autistic adults;
To examine relationships between these study variables and age; and
To examine the involvement of IU as a mediator
between the sensory sensitivities, repetitive behaviours and anxiety, based on existing findings
involving younger individuals on the spectrum
(Figure 1).
3
Hwang et al.
It was hypothesised that autistic adults would have
higher scores on the study variables relative to those from
the general population, and that the relationships between
these study variables as visualised in Figure 1, would be
replicated for an adult sample. Given restricted available
evidence, the only hypothesised relationship between
these study variables and age was an expected decrease in
both types of restricted, repetitive behaviours with age.
Methods
Participants
Participants were adults on the autism spectrum and a
community comparison sample of non-autistic adults who
participated in the first wave of the Australian Longitudinal
Study of Adults with Autism (ALSAA) funded by the
Cooperative Research Centre for Living with Autism
(Autism CRC). The ALSAA is a questionnaire-based study
including a comprehensive range of standardised and nonstandardised measures of health, functioning and participation for autistic adults in Australia (ages 25 and over).
Ethical approval for the study has been granted by the
University of New South Wales Human Research Ethics
Committee. More detail about the protocol for the ALSAA,
including its inclusive research approach, is described
elsewhere (Arnold et al., 2019).
ALSAA participants were recruited via promotional
materials, including both paper and online flyers, which
were dispersed via mail and email to a range of autismspecific organisations, aged-care and disability service
providers, community newspapers, universities, medical
centres and relevant online communities. Participants
expressed interest via email, telephone or an online form.
Interested participants were screened for eligibility before
being sent either a paper questionnaire or a personalised
link to the online questionnaire on Qualtrics (2018), a
web-based survey platform. Both versions of the questionnaire were preceded by an information statement and consent form specifying that completing and returning the
questionnaire implied informed consent.
Participants for this study included 214 autistic adults
from the ALSAA who self-reported a clinical diagnosis of
ASD with a score over 65 on the Autism-Spectrum
Quotient-Short (AQ-short; Hoekstra et al., 2011) and 146
non-autistic adults. Inclusion criteria included being
25 years old or older, living in Australia and sufficient
English proficiency to complete the questionnaire. Of this
initial sample, 38 (18%) autistic participants and 30 (20%)
non-autistic participants had incomplete data for the study
variables. Chi-square tests and independent samples
t-tests revealed no association between missing observations and being autistic (p = 0.40), age (p = 0.21), gender
(p = 0.63) or scores on measures of IU (p = 0.23), anxiety
(p = 0.96) or sensory sensitivities (p = 0.29). Therefore,
only 176 autistic adults and 116 non-autistic adults with
complete data were considered for analysis.
Measures
Sample characterisation. Information regarding age, gender, type of autism diagnosis and current anxiety diagnosis was collected as part of the ALSAA. Self-reported
intellectual disability status and severity was also collected (none, mild, moderate, severe, profound). In addition, data from four self-reported measures were used in
this study.
Intolerance of uncertainty. The intolerance of uncertainty
scale-12 (IUS-12; Carleton et al., 2007) is an abridged version of the 27-item IU scale. Participants rate items regarding aversion and reactions to change or unforeseen events
(e.g. ‘Unforeseen events upset me greatly’, ‘When it is
time to act, uncertainty paralyses me’) on a 5-point Likerttype scale ranging from 1 ‘Not at all characteristic of me’
to 5 ‘Entirely characteristic of me’. Higher scores indicate
higher levels of IU. In non-autistic adults, the scale has
been found to have good test–retest reliability and construct validity against other symptom measures of worry,
depression and anxiety (Buhr & Dugas, 2006). Internal
reliability for this sample was strong for both samples
(Cronbach’s α = 0.88–0.92).
Sensory sensitivities. The Glasgow Sensory Questionnaire
(GSQ; Robertson & Simmons, 2012) is a measure of sensory sensitivities commonly reported by those on the spectrum. The 42-item measure contains an even split of
questions measuring hyper- and hypo-sensitivity, with six
questions dedicated to each of the seven common sensory
modalities: visual; auditory; gustatory; olfactory; tactile;
vestibular and proprioceptive. Participants respond to the
frequency of certain sensory experiences on a 5-point scale
(0 – Never to 4 – Always). Scores can be computed for
total sensory sensitivity, hyper- and hypo-sensitivity, with
higher scores indicating greater sensitivity. Internal reliability for the autistic (α = 0.93) and non-autistic adult
(α = 0.91) samples were high.
Anxiety. The American Psychiatric Association’s (2013)
Severity Measure for Generalised Anxiety Disorder
(GAD) provides a dimensional assessment of GAD in
adult populations as defined in the fifth revision of the
Diagnostic and Statistical Manual of Mental Disorders.
The measure consists of 10 items describing a state indicative of clinical GAD as of the past 7 days. These items
describe a range of visceral, intellectual and behavioural
reactions that evidence the state of anxiety (e.g. ‘I have felt
moments of sudden terror, fear or fright’, ‘I sought reassurance from others due to worries’) Participants rate how
frequently they experienced these items during the past
4
Autism 00(0)
7 days on a 5-point scale (0 – never to 4 – all of the time).
Internal reliability for the autistic (α = 0.90) and non-autistic adult (α = 0.90) samples were high. The scale has demonstrated good sensitivity (0.87) and specificity (0.73) and
strong convergent and discriminant validity when compared with the previously validated 7-item scale (r = 0.80,
p < 0.01; Beesdo-Baum & Knappe, 2012). A cutoff score
of 14 indicates clinically significant anxiety.
a mediation analysis was conducted with IU as a mediator
of autism diagnosis and anxiety for the entire sample (both
autistic and non-autistic adults; Figure 2(a); Neil et al.,
2016; Wigham et al., 2015).
In addition to this, the mediating role of IU between the
study variables and anxiety was tested for the autistic
group only (Figure 2(b) and (c)). These were based on the
exploratory framework presented in Figure 1.
Repetitive behaviours. Restricted and repetitive behaviours
were measured via the Repetitive Behaviours Questionnaire-2 for adults (RBQ-2A; Barrett et al., 2015) which is
an adaptation of the Repetitive Behaviour Questionnaire-2
(Leekam et al., 2007) for use in adults. The RBQ-2A consists of 20 items divided into five sections. Items in three
of the sections are rated on a 4-point scale, while the
remaining items use a 3-point scale. Higher scores indicate
higher likelihood or frequency of engaging in restricted
and repetitive behaviours. Previous work has found the
measure to consist of two factors: repetitive motor behaviours and insistence on sameness. Insistence on sameness
captures a preference for uniformity or consistency (e.g.
‘like to arrange items in rows or patterns’), while repetitive
sensory–motor behaviours refer to behaviours which are
repeated (e.g. ‘spin yourself around and around’). The
RBQ-2A has displayed good psychometric properties in a
sample of autistic adults (Barrett et al., 2015). Internal reliability for the autistic (α = 0.90) and non-autistic adult
(α = 0.78) samples were high in this study.
Inclusive research approach. Following initial interpretation of the findings by the researchers, further insight and
feedback regarding these findings and interpretations
were sought from six autistic adults who were part of the
ALSAA advisory panel. A plain English summary of the
findings and possible interpretations were emailed to
these advisors, who were given 1 month to give their feedback. Feedback could be given via reply email, video, telephone or video conferencing. Autistic advisors were
offered reimbursement for their time. Insights gained
from the feedback were incorporated into the discussion
of the findings.
Statistical analysis
Descriptive statistics, such as means, standard deviations and
frequencies, were used to examine demographic characteristics and scores on the study variables for autistic adults and
non-autistic adults. Chi-square tests and independent t-tests
with Bonferroni-adjusted significance levels were run to
examine differences in the study variables between autistic
and non-autistic adults. Pearson’s correlations were used to
explore associations between the study variables, age and
gender. A series of linear regressions were used to further
investigate significant associations between the study outcome variables and age. STATA statistical software version
14 (StataCorp, 2015) was used for the above analyses.
In order to replicate the relationships found between the
study variables for existing studies examining younger
autistic groups, five mediation analyses were conducted.
All mediation analyses were conducted using the PROCESS
macro in SPSS (Statistical Package for Social Science, version 22). Bootstrapping (1000 resamples) with bias-corrected and accelerated 95% confidence intervals (BCa)
used to adjust for measurement error. The Sobel test was
used to determine the significance of the mediation effect.
First, in order to replicate findings of past studies regarding IU as a key mediator of anxiety in autistic individuals,
Results
Participant demographics are available in Table 1. Our
sample included a total of 292 participants (176 autistic
and 116 non-autistic adults). The mean age of autistic
and non-autistic adults was comparable. Approximately
40% of autistic adults were male, while the non-autistic
adult sample was predominantly female. A significantly
higher proportion of autistic adults (57.7%) reported
having a current diagnosis of anxiety than non-autistic
adults (14.0%). Five participants had one item from the
AQ missing and one participant had two items from the
AQ missing. Total scores were imputed for these six
participants by adding their total score to: (mean score
for non-missing items × number of missing items).
Significant differences were found on the GAD scores
between those with and without self-reported anxiety
diagnosis for both autistic (p < 0.001) and non-autistic
adults (p < 0.001).
Between groups differences
Table 2 presents the scores on measures of IU, anxiety,
sensory sensitivity and repetitive behaviours for autistic
adults in comparison with non-autistic adults. The AQ
scores for the non-autistic comparison sample were notably high. This may reflect the self-selecting sample, which
may have included extended family and friends of those on
the spectrum. Studies involving relatives of those on the
spectrum suggest a significant subset to display ‘milder’,
subclinical autism traits – described by the term ‘broad
autism phenotype’ (Wallace, Budgett, & Charlton, 2016).
Despite this, and in line with previous studies, autistic
5
Hwang et al.
Figure 2. (a) IU as a mediator between ASD diagnosis and anxiety, (b) IU as a mediator between hyper- and hypo-sensitivity
and anxiety in autistic adults and (c) IU as a mediator between anxiety and repetitive behaviours (both repetitive sensory–motor
behaviours and insistence on sameness) in autistic adults.
Table 1. Demographic characteristics of autistic participants and non-autistic adults.
Age, M (SD; range)
Male, N (%)
Intellectual disability, N (%)
AQ-short score, M (SD)
Current anxiety diagnosis, N (%)
ASD (N = 176)
Non-autistic adults (N = 116)
p
41.7 (12.8; 25–78)
67 (39.9)
8 (4.5)
89 (9.42)
98 (57.7)
43.0 (13.2; 25–77)
25 (21.6)
1 (0.8)
55 (11.6)
16 (14.0)
0.390
<0.001
0.092
<0.001
<0.001
ASD: autism spectrum disorder; PDD NOS: pervasive developmental disorder not otherwise specified.
‘Other’ diagnoses include autistic disorder, PDD NOS and infantile autism.
adults reported significantly greater levels of all variables
of interest compared with non-autistic adults.
Correlations
Pearson’s correlations between age, gender and study variables are displayed for autistic and non-autistic adults in
Tables 3 and 4, respectively. For autistic adults, moderate to
strong positive correlations were found between the study
variables (r = 0.27–0.73). In general, the strongest associations were found among repetitive behaviours (total and subscales) and sensory sensitivities (total and subscales;
r = 0.58–0.73). Strong associations were found within scores
on the total and subscale scores for sensory sensitivities
6
Autism 00(0)
Table 2. Differences between autistic participants and non-autistic adults on scores for IU, anxiety and sensory sensitivities.
IU M (SD; range)
Total sensitivity
M (SD; range)
Hypersensitivity
M (SD; range)
Hyposensitivity
M (SD; range)
Anxiety
M (SD; range)
Total repetitive behaviours
M (SD; range)
Repetitive sensory–motor
M (SD; range)
Insistence on sameness
M (SD; range)
Autistic (N = 176)
Non-autistic adults
(N = 116)
Possible score range
p
41.8
(10.4; 14–60)
78.4
(25.7; 1–147)
43.2
(15.1; 0–79)
33.2
(11.4; 1–65)
14.5
(8.4; 0–38)
36.7
(8.4;19–56)
1.7
(0.49; 1–2.8)
2.1
(0.48;1–3)
24.3
(7.7; 12–50)
34.9
(17.3; 0–107)
19.8
(9.7; 0–66)
14.4
(8.4; 0–39)
5.6
(5.5; 0–29)
22.6
(3.5; 19–33)
1.1
(0.15; 1–1.8)
1.2
(0.26;1–2)
12–60
<0.001*
0–168
<0.001*
0–84
<0.001*
0–84
<0.001*
0–40
<0.001*
19–57
<0.001*
1–3
<0.001*
1–3
<0.001*
SD: standard deviation.
*p < 0.0063 (Bonferroni-adjusted).
Table 3. Pearson’s correlations between age, gender and study variables for autistic participants (N = 176).
Age
Age
1
−0.15
Gendera
IU
−0.13
Anxiety
−0.19
Total ss
−0.20
Hyper-ss
−0.14
Hypo-ss
−0.26*
Repetitive behaviours
−0.28*
Repetitive sensory–motor −0.36*
Insistence on sameness
−0.21
Gendera IU
1
0.09
0.12
0.32*
0.40*
0.16
0.15
0.16
0.13
1
0.55*
0.34*
0.36*
0.27*
0.50*
0.34*
0.53*
Anxiety Total ss Hyper-ss Hypo-ss Total
Repetitive
repetitive sensory–
behaviours motor
1
0.38*
0.38*
0.33*
0.49*
0.44*
0.46*
1
0.96*
0.92*
0.73*
0.67*
0.64*
1
0.76*
0.65*
0.58*
0.59*
1
0.73*
0.69*
0.63*
1
0.84*
0.95*
1
0.65*
Insistence on
sameness
1
aPositive indicates female gender.
*p < 0.005 (Bonferroni adjustment).
(r = 0.76–0.96). For repetitive behaviours, a smaller association was found between the two subscales, reflecting the distinct two-factor structure of this scale reported in previous
studies (Barrett et al., 2015). IU had the strongest associations with anxiety (r = 0.55) and insistence on sameness
(r = 0.53), and weaker associations with hyposensitivity
(r = 0.27) and repetitive sensory–motor behaviours (r = 0.34).
Regarding demographic variables, age of autistic adults was
found to have significant negative associations with hyposensitivity (r = −0.26), total repetitive behaviours (r = −0.28)
and repetitive sensory–motor behaviours (r = 0.38). Female
gender had moderate positive associations with total- and
hyper-sensitivity.
A similar pattern of associations was found for nonautistic adults. Weak to moderate correlations were found
between study variables (r = 0.26–0.65), the highest association being that between IU and anxiety (r = 0.65).
Similar to the autistic group, high associations were found
between the total score and subscale scores for sensory
sensitivities (r = 0.73–0.93) and a smaller association
between the two RBQ-2A subscales. No significant correlations were found between these variables and demographic variables of age and gender.
Associations between age and study variables
Given the significant associations found between age and
the study variables presented in Table 3, a series of linear
regressions were conducted with age as the predictor
of hyposensitivity, repetitive behaviours and repetitive
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Hwang et al.
Table 4. Pearson’s correlations between age, gender and study variables for non-autistic adult participants (N = 116).
Age
Gendera IU
Age
1
−0.03 1
Gendera
IU
−0.15 −0.01
Anxiety
−0.04 0.14
Total ss
0.04 −0.11
Hyper-ss
0.03 0.06
Hypo-ss
0.04 −0.25
Total repetitive behaviours −0.13 −0.09
Repetitive sensory–motor −0.17 −0.07
Insistence on sameness
−0.10 −0.08
Anxiety Total ss Hyper-ss Hypo-ss Total
Repetitive
repetitive sensory–
behaviours motor
1
0.65* 1
0.30* 0.28*
0.32* 0.28*
0.26* 0.23
0.43* 0.42*
0.37* 0.39*
0.37* 0.35*
1
0.93*
0.93*
0.59*
0.47*
0.48*
1
0.73*
0.48*
0.41*
0.37*
1
0.62*
0.45*
0.53*
1
0.60*
0.94*
1
0.32*
Insistence on
sameness
1
aNegative indicates male gender.
*p < 0.005 (Bonferroni adjustment).
Table 5. Direct and indirect effects from the mediation models involving IU.
Model Sample
1
Predictor
Mediator(s) Outcome
R square Total effect (B),
SE [95% CI]
Anxiety
0.51
2
ASD & non- ASD
IU
autistic adults
ASD
Hypersensitivity IU
Anxiety
0.38
3
ASD
Hyposensitivity IU
Anxiety
0.37
4
ASD
Anxiety
IU
5
ASD
Anxiety
IU
Repetitive
0.30
sensory–motor
Insistence on 0.34
sameness
Direct effect (B), Indirect effect (B),
SE [95% CI]
SE [95% CI], p
17.15, 1.15
0.80, 0.96
7.77, 0.82
[14.90, 19.41]*** [−1.08, 2.69]
[6.19, 9.40]***
0.22, 0.04
0.11, 0.04
0.10, 0.02
[0.13, 0.29]***
[0.04, 0.18]*** [0.06, 0.15]***
0.26, 0.05
0.15, 0.05
0.11, 0.03
[0.16, 0.36]***
[0.05, 0.24] ** [0.05, 0.18]***
0.03, 0.004
0.02, 0.005
0.005, 0.003
[0.02, 0.03]***
[0.01, 0.03]*** [0.001, 0.01]
0.03, 0.004
0.01, 0.004
0.013, 0.003
[0.02, 0.04]***
[0.006, 0.023]** [0.008, 0.019]***
CI: bootstrapped confidence interval; B: beta coefficient; ASD: autism spectrum disorder.
Models 2–5 were adjusted for age and gender.
**p < 0.01; ***p < 0.001.
sensory–motor behaviours. Hyposensitivity (b = −0.24,
95% CI = −0.37, −0.11, p = 0.001), total repetitive behaviours (b = −0.18, 95% CI = −0.28, −0.08, p = <0.0001) and
repetitive sensory–motor behaviours (b = −0.14, 95%
CI = −0.02, −0.01, p < 0.0001) were all predicted by age.
accounted for (mediated by) IU. For Models 2–5, a sensitivity analysis was conducted for age using two age groups
(<40 and 40+; N = 87 and 88). No differences were found
for any of the models in the two age groups regarding the
significance of IU as a mediator.
Mediation models
Discussion
Results of the five mediation models (Figure 2(a) to (c))
are presented on separate rows in Table 5. Of interest are
the indirect effects for each of the mediation models, with
a significant indirect effect (p < 0.05) suggesting that the
observed relationship between the predictor and outcome
variable is at least partially explained by the mediator (IU).
IU was found to be a significant mediator in all models
except in the relationship between anxiety and repetitive
sensory–motor behaviours (Model 4). The lack of a significant direct effect in Model 1 indicates that the relationship between autism status and anxiety may be fully
Overall, these findings support the central role of IU in the
interrelationships between anxiety and autism traits for
autistic adults aged 25 and older. Significant positive correlations between these study variables replicate similar
findings in children and younger adults (Neil et al., 2016;
Wigham et al., 2015). Also consistent with the findings in
children (Boulter et al., 2014; Neil et al., 2016), adults on
the spectrum had significantly higher IU and anxiety than
those not on the spectrum. Self-reported rates of anxiety
were high in this sample (58%) and similar to those in published studies of autistic adults (Buck et al., 2014; Joshi
8
et al., 2013). Sensitivity analyses suggest that, although a
decline in repetitive behaviours is evident, these relationships between the study variables hold for both older
(40+) and younger (<40) adults.
As with existing studies, a decline in repetitive
behaviours was found with age (Levy & Perry, 2011).
Specifically, a significant decrease was found in sensory–
motor behaviours, hyposensitivity and repetitive behaviours overall. Although statistically significant, the effect
sizes for hyposensitivity and total repetitive behaviours are
small when considered in light of the scales, that is, two
autistic adults 10 years apart in age are expected to have a
difference of 2.4 on their hyposensitivity as measured by
the GSQ (possible score range 0–128). The observed
decline in repetitive sensory–motor behaviours was arguably more substantial. Autistic individuals may learn with
experience or as a result of targeted therapies, to ‘mask’
these behaviours to appear more socially acceptable (Cage,
Di Monaco, & Newell, 2018; Dean, Harwood, & Kasari,
2017). Despite a decline, these behaviours are still apparent in adulthood.
Given the heterogeneity of the autism spectrum, further
work is needed to clarify the reasons for this apparent
decline as well as whether and why certain adults may
have reduced repetitive behaviours while others do not,
especially in older adults for whom research is scarce. An
alternative explanation may be that autistic adults may
develop other means of fulfilling their need for repetition
through other activities. Experiences of behavioural intervention may also contribute to this decline. Taken together,
these findings agree with existing beliefs that despite evidence of some reduction in traits over time, most autistic
individuals remain on the spectrum in adulthood (Howlin
& Magiati, 2017; Levy & Perry, 2011).
The first mediation analysis was able to replicate findings in younger samples regarding the central role of IU in
the anxiety of those on the spectrum in comparison with
those from the general population (Boulter et al., 2014;
Neil et al., 2016). Further, the results suggest IU to be an
important mechanism underlying the relationship between
anxiety and sensory sensitivities (both hyper- and hyposensitivity), as well as between anxiety and insistence on
sameness. Of note was our finding of a lack of a mediation
effect of IU on the relationship between anxiety and repetitive sensory–motor behaviours. In line with this, existing
literature has converged on ideas that directly link repetitive sensory–motor behaviours with sensory sensitivities
(e.g. modulation of sensory arousal) and anxiety (e.g. coping with anxiety; Joyce et al., 2017; Leekam et al., 2007).
Implications
For adults on the autism spectrum, anxiety and anxietyprovoking experiences are common in day-to-day life
(Cage et al., 2018; Hare, Gracey, & Wood, 2016). These
Autism 00(0)
may be the effect of a range of factors, including a lack of
self-efficacy in navigating healthcare systems (Maloret &
Scott, 2018; Nicolaidis et al., 2013), where a range of barriers such as lack of clinician training exist (Warfield,
Crossman, Delahaye, Der Weerd, & Kuhlthau, 2015), as
well as negative experiences in employment, including
underemployment and employment instability (Eaves &
Ho, 2008; Tobin, Drager, & Richardson, 2014). While past
studies present important suggestions for environment and
system-level changes to improve the mental health of
autistic adults, the present findings also present the potential for addressing an individual-level factor, IU, as a
method of managing elevated anxiety levels in this population. This may offer a more sustainable method of decreasing anxiety than efforts to minimise uncertainty in the
autistic individual’s life environment.
The findings suggest that interventions for reducing
anxiety in autistic adults should target IU, which has been
the target of interventions that have successfully reduced
anxiety severity in non-autistic adults and children
(Boswell, Thompson-Hollands, Farchione, & Barlow,
2013; Buhr & Dugas, 2009; Dugas et al., 2010). In autistic
individuals, IU is receiving increased attention. One study
of autistic children reported IU to impact treatment response
to modified cognitive behavioural therapy, with higher levels of pre-intervention IU predicting higher anxiety both
pre- and post-intervention (Keefer et al., 2017). One manualised treatment programme targeting IU has been examined for a small sample of autistic adolescents (Rodgers
et al., 2017) and adults (Rodgers, Herrema, Honey, &
Freeston, 2018) with promising results regarding effectiveness and acceptability. The present findings suggest that
such interventions may have a follow-on effect on insistence on sameness behaviours in autistic adults and may
have additional benefits for those with sensory sensitivities
above interventions that do not address IU.
In developing such interventions, it is important to consider the practical, psychological and communicative factors implicated in delivering effective mental healthcare to
adults on the spectrum. Emerging research suggests the
presence of alexithymia, a difficulty in recognising and
describing one’s own emotional states, is increased in
autistic individuals and is directly related to anxiety
(Maisel et al., 2016). In a similar vein, the presence of psychiatric comorbidities, such as attention-deficit hyperactivity disorder (ADHD) in this population (Lever & Geurts,
2016) may further complicate the delivery of interventions. Accordingly, interventions should be appropriately
designed to account for such differences and careful consideration of the effect of these conditions on the therapy
should be considered.
More broadly, the comfort and effectiveness of the
intervention experience may be improved through accommodations such as involvement of a support person and
allowing diverse methods of communication (Nicolaidis
Hwang et al.
et al., 2015; Robertson et al., 2018). One recent study
observed psychotherapy outcomes in a college counselling
setting for 76 autistic adults and concluded that while
desirable outcomes may be achieved with psychotherapy,
autistic adults may require more extended treatment periods and have unique communication needs compared with
non-autistic adults (Anderberg et al., 2017). Such findings
are important for considering the impact of session caps
and counselling techniques for autistic populations.
Further, it is important to acknowledge the heterogeneity in the precipitators and presentation of sensory
sensitivities, repetitive behaviours and anxiety in autistic
individuals (Barrett et al., 2015; South & Rodgers, 2017;
Uljarević et al., 2017). Autism is a spectrum condition,
and qualitative literature also attests to the variety of
experiences related to anxiety that autistic individuals
are exposed to (Robertson et al., 2018). As such, a onesize-fits-all approach to intervention will be limited in
its effect. Further work, especially that which focuses on
the different trajectories of these factors into middle and
late adulthood, will be useful for targeting interventions
appropriately.
Limitations and future work
This study is the first examination of the theoretical relationships between IU, anxiety, sensory sensitivities and
repetitive behaviours for adults on the autism spectrum.
The findings are most representative of those on the spectrum without intellectual disability. At present, findings are
inconsistent and sparse regarding the prevalence of anxiety,
and the prevalence of other study variables in those with
intellectual disability versus without (Crane et al., 2009;
Sterling, Dawson, Estes, & Greenson, 2008; van Steensel,
Bogels, & Perrin, 2011) with a noted lack of studies exploring the former (Rodgers & Ofield, 2018). Further studies
focusing on those with intellectual disability are needed.
These findings also rely on the accurate self-reporting
of symptoms by ALSAA survey participants. Self-report is
arguably most suitable for measuring repetitive behaviours, sensory processing and IU in adults. Regarding anxiety, given the use of psychometrically sound scales and no
need for distinction between clinical or sub-clinical levels
of anxiety, self-report was also deemed sufficient for the
present analysis. Clinically assessed or validated anxiety
scores may be of interest for future studies, particularly
those that investigate the effects of intervention.
Clinical validation of the autism sample was not feasible for the present nationwide longitudinal study and the
findings are thus limited by the self-reporting of autism
status. Only self-reported intellectual disability status was
collected. Although there was reliance on self-report, participants were required to explicitly indicate their receipt
of a formal diagnosis at the commencement of the survey,
with other options including ‘I do not have a formal
9
diagnosis but think I have autism’. Autistic adults were
then required to report which year they received this diagnosis, the specific diagnosis they received, and the name
and profession of the diagnosing clinician(s). This
approach, combined with the time-intensive (2–3 h) nature
of the survey and absence of participant reimbursement,
minimised the likelihood of participation by those who did
not meet inclusion criteria for the study. Furthermore, participants who expressed that they did not receive a formal
diagnosis, and those with scores below the AQ cutoff,
were not included in this study. This method of self-report
coupled with the AQ-short was deemed appropriate by the
autistic advisory panel, and has also been argued as appropriate for research that may be generalised to all adults
who identify as autistic (Bal & Lounds Taylor, 2019). This
approach allows for the ‘lost generation’ of middle-aged
and older autistic adults (Lai & Baron-Cohen, 2015) who
experience significant barriers to diagnosis.
A gender bias towards females was apparent in this
sample, which is contrary to the established gender ratio
for autistic samples (Halladay et al., 2015). This is a commonly evidenced phenomenon in online research with
self-selecting samples (Guo, Kopec, Cibere, Li, &
Goldsmith, 2016) and has been true of other online survey
studies involving those on the spectrum (Gilmour,
Schalomon, & Smith, 2012; Nicolaidis et al., 2013).
Studies have inconsistently reported gender differences
regarding sensory sensitivities and repetitive behaviours
(Antezana et al., 2019; Bitsika, Sharpley, & Mills, 2018),
and further research may be useful in understanding their
presentation and relationship to anxiety. The present analyses were adjusted for the effects of gender.
Moving forward theoretically, studies that are experimental in nature with improved ecological validity are
needed in order to disentangle the causal relationships
between the study variables. Importantly, to increase
the validity of such work, focused investigations of the
psychometric properties of IU and anxiety measures,
and their validation for use with autistic adults, are
needed. This study was a cross-sectional examination
of the role of IU in the present levels of anxiety and
autism characteristics in the sample. History of involvement in therapeutic interventions for anxiety, and relevant medication use was not examined. Future studies,
especially those that may consider the effect of interventions for anxiety should consider the effect of medication use and other therapies.
Finally, there will be a wealth of lived experience on the
part of autistic adults and carers who have experienced
these symptoms over many years, developed their own
coping mechanisms and experienced a range of therapies
and health systems over their lifetimes. These will be
important to consider for designing and implementing
effective, appropriate and accessible interventions for the
reduction of anxiety in future.
10
Autism 00(0)
Conclusion
IU is an important factor to be considered in the conceptualisation and management of elevated rates of anxiety for
adults on the autism spectrum, as is the case for children
and young adults. Sensory sensitivities and repetitive
behaviours are also implicated in anxiety. Continued
development of targeted interventions for managing IU in
autistic adults will be useful for managing anxiety. Future
work should involve those with lived experience, and
should focus on the validation of measures for autistic
adults as well as experimental investigations of the causal
relationships between study variables. These will help
inform the development and adaptation of interventions
for adults on the spectrum.
Acknowledgements
We are grateful for the contribution and participation of all adults
on the autism spectrum and their carers involved in the ALSAA.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect
to the research, authorship and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support
for the research, authorship and/or publication of this article:
This work was supported by the Cooperative Research Centre for
Living with Autism (Autism CRC), established and supported
under the Australian Government’s Cooperative Research
Centres Program.
ORCID iD
Ye In (Jane) Hwang
https://orcid.org/0000-0003-0142-3251
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