Interventions for anxiety in mainstream school‐aged children with autism spectrum disorder: A systematic review

(RCTs) and six quasi ‐ experimental studies met the inclusion criteria. These studies evaluated the effects of


| What is this review about?
Anxiety is a common problem in school-aged children with ASD. CBT and other psychosocial interventions have been developed as alternatives to pharmacological intervention to treat anxiety in students with ASD.

What is the aim of this review?
This Campbell systematic review examines the effects of interventions for reducing anxiety in school-aged children with ASD, compared to treatment-as-usual. The review summarizes evidence from 24 studies using an experimental or quasi-experimental design.

| What studies are included?
Twenty-four studies, involving 931 school-aged children with ASD (without co-occurring intellectual disability) and clinical anxiety, are No adverse events were reported. Given the nature of the interventions and the selected outcome measures, the risk of performance and detection bias are generally high, particularly for those studies that used outcome measures based on parent and self-reports.

| Authors' conclusions
There is evidence that CBT is an effective behavioral treatment for anxiety in some children and youth with ASD without co-occurring intellectual disability. Evidence for other psychoeducational interventions is more limited, not just due to the popularity of CBT but also due to the quality of the smaller number of non-CBT studies available.
While there is evidence that CBT is an effective behavioral treatment for anxiety in some children and youth with ASD, work remains to be done in terms of identifying the characteristics of these interventions that contribute to their effectiveness and identifying the characteristics of participants who are more likely to respond to such interventions.
3 | BACKGROUND 3.1 | The condition ASD refers to a group of neurodevelopmental disorders characterized by difficulty with communication and social interaction, and the presence of restricted, rigid, and routinized patterns of behaviors and interests (American Psychiatric Association, 2013). These symptoms appear on a continuum (or spectrum), with some children experiencing relatively mild symptoms, while others experience quite severe symptomatology. Notwithstanding the changing ways in diagnosing children with ASD, the reported prevalence appears to be increasing over time (ABS, 2016;Fombonne, 2018). For example, the current rate of prevalence in the United States (US) has reportedly risen by 15% over recent years to 1 in 59 (Autism Speaks, 2016;Baio et al., 2018;CDC, 2012), while in Australia, the rate has increased by 42% between 2012 and 2016, to 1 in 150 children (ABS, 2016).
In addition to increasing numbers, recent research shows that the number of students with ASD attending mainstream schools is also increasing (Zainal & Magiati, 2016). The exact reason for the increase in prevalence is unclear, but may be related to changes in the Diagnostic and Statistical Manual of Mental Disorders (DSM; American Psychiatric Association, 2013; Fombonne, 2018), as well as increased awareness and better recognition of borderline cases that were otherwise previously diagnosed as anxiety, bipolar, or other related disorders.

| Anxiety in ASDs
Anxiety is characterized by fear. Symptoms can include somatic complaints, such as stomach ache, headache, sleeplessness, and diarrhea, as well as other symptoms including tiredness, irritability, and difficulty concentrating (Beyondblue, 2017). Some level of anxiety is normal. However, when the fear is persistent, excessive and interferes with one's ability to function normally, a diagnosis of an anxiety condition may be warranted.
Although the reported rate of anxiety for those with ASD varies widely (e.g., from 13% to 84%), the majority of studies suggest that a realistic estimate is between 40% and 50% ( van Steensel, Bögels, & Perrin, 2011).
The majority of studies undertaken exploring anxiety and ASD have focused on very young children, or older adolescents and adults.
Fewer studies have been undertaken with school-aged children, but those studies that have been conducted suggest a high co-occurrence of anxiety in ASD populations of this age group (Ashburner, Ziviani, & Rodger, 2010;Gjevik, Eldevik, Fjaeran-Granum, & Sponheim, 2011;Lecavalier, 2006). The prevalence of anxiety among school-aged children is of particular concern considering that anxiety during this HILLMAN ET AL.

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period has a negative impact on intellectual functioning and academic achievement, and broadly on a child's overall school-functioning (Mazzone et al., 2007;Wood, 2006). School may present students with ASD particular cognitive, social and behavioral challenges that may increase levels of anxiety, and conversely, increased anxiety can impair school-functioning. In addition, teachers tend to perceive students with ASD as having more difficulty with academic success and with anxiety than their typically developing peers (Ashburner et al., 2010). Additional studies of children with an ASD have shown that anxiety negatively impacts a child's ability to participate in home, school, and community settings, and effects child and family well-being and quality of life above and beyond the core symptoms of ASD (Davis, White, & Ollendick, 2014;Pellecchia et al., 2016).
Anxiety also has long term impacts. If left untreated, anxiety persists into adulthood and can progress into other disorders, such as depression (Seligman & Ollendick, 1998;US Public Health Service, 2000). Moreover, chronic anxiety is related to reduced employment opportunities and social networks, and thus is associated with the societal and economic burden (Davis, Ollendick, & Nebel-Schwalm, 2008;Velting, Setzer, & Albano, 2004).
While it may sometimes be difficult to distinguish between the characteristics of ASD and the characteristics of anxiety, this review assumes that a change in anxiety levels as indicated by changes in standardized and validated measures of anxiety while the diagnosis of ASD remains can be taken as an indicator of a treatment effect on anxiety.

| The intervention
Interventions and programs that aim to address anxiety and the challenges that school-aged children with ASD face in educational environments, may improve their overall school-functioning and later life outcomes. Against this background, the need for accurate treatment of anxiety in school-aged children with ASD is evident. There are numerous interventions currently available for the treatment of anxiety in children and young people.
The focus of this review is on interventions designed to help a child's functioning in real-world settings such as school and the home, although treatment or interventions may be located in a range of settings, including schools, the home, online, and research and support centers. Thus, studies assessing only the impact of pharmacological interventions were excluded, while a study investigating the impact of CBT on academic performance would be included. Research indicates CBT is useful for treating anxiety disorders, but less is known about its efficacy in treating anxiety within ASD populations (Nadeau et al., 2011). 3.4 | How the intervention might work Rotheram-Borus, Swendeman, and Chorpita (2012) proposed that all existing interventions for anxiety incorporate one or more of the following seven elements: (a) psychoeducation, (b) exposure, (c) cognitive restructuring, (d) parent training or parent psychoeducation, (e) relaxation, (f) modeling, and (g) self-monitoring.
CBT is a relatively popular alternative to pharmacological intervention for anxiety symptoms that incorporates a number of these elements. At its core, CBT involves, as the name suggests, cognitions or thoughts and how these may contribute to or alleviate anxiety, and behavior or how a person might behave or respond to a situation or experience that may trigger anxiety, as well as how these cognitions and behavior interact. A CBT-based intervention for young people with ASD and anxiety will probably include educational sessions for the young people, and possibly their parents, about negative thought patterns and cognitive distortions such as "catastrophising" and how these contribute to anxiety (psychoeducation and parent psychoeducation/training) and how to challenge these thought patterns (cognitive restructuring). These sessions might also be combined with other types of intervention like supported exposure to situations that the young people have previously found anxiety-provoking, such as social interactions, with coaching sessions on how to monitor their thoughts, and to recognize and control physical reactions to stress and anxiety (self-monitoring and relaxation).
Previous research has indicated that CBT can be effective and efficient in treating anxiety in children and youth as well as adult populations (Kaczkurkin & Foa, 2015;Kendall & Southam-Gerow, 1996;Otte, 2011), but the core features of ASDs must be considered when determining whether and how the treatment might be appropriate for use with ASD populations. Some characteristics of CBT, such as its highly-structured, pragmatic focus on current problems may align with features of ASD such as increased need for structure and order, while other aspects such as reliance on verbal communication with the therapist, insight in one's own thoughts, feeling and actions, and recognition of emotions in oneself and others, may prove challenging for some clients with ASD. For these reasons, many CBT-based treatments for anxiety have been modified specifically for use with ASD populations, including such considerations as replacing group sessions with one-on-one treatments sessions, increasing the amount of time dedicated to engagement with the therapist, increasing the number of sessions dedicated to emotion recognition training, adapting activities, and worksheets to the specific strengths and weaknesses of the clients or incorporating clients' special interests into treatment where appropriate (NICE, 2013).

| Why it is important to do the review
Since children spend a significant portion of their day at school, teachers and clinicians working in the education sector have significant responsibility for recognizing signs of ASD and anxiety, and in implementing interventions and supports that are evidence-based and tailored to the needs of the child. Further, decision making regarding treatment should be informed by the latest evidence available.
However, none of the reviews published thus far have: (a) focused specifically on school-aged children with ASD; (b) covered the range of available treatments, but instead focused only on specific treatments, such as, for example, CBT or psychosocial treatments; (c) explored mediators and moderators of treatment outcomes; and (d) provided practical guidance for education professionals and parents to enable increased use of evidence-based treatments in their everyday practice.
Accordingly, this review aimed to synthesize evidence about interventions to reduce anxiety symptoms in school-aged children with ASD. While clinical studies were not excluded per se, this review sought to move beyond interventions that were relevant only for clinical practice and care in clinical settings, and prioritized studies that drew out implications for school-aged children that would help their functioning in real-world settings such as school and the home.
To achieve this aim, the review employed a quantitative (experimental and quasi-experimental) approach, in order to establish evidence of impact (Joanna Briggs Institute, 2014).

| The problem
The sheer volume of published research, and the different aims, foci, and methodology of those studies, makes evidence-based practice difficult for professionals, including for those working in the education sector. The current review contributes to providing consolidated sources of information for professionals. Results of the review are intended to inform professionals working in the education sector and parents, but may also inform policymakers in this sector.
Hence, this review aimed to address the following research question.
1. What is the relative effectiveness of interventions for managing anxiety of school-aged children with ASD that have been used in school, family, and clinical settings?
In the process, this review also identified the following: • The interventions used for managing anxiety of school-aged children with ASD in school, family, and clinical settings.
• The evidence-based practices that school staff, parents, and other professionals can employ to mitigate anxiety-related symptoms in school-aged children with ASD. 5 | METHODS 5.1 | Criteria for considering studies for this review 5.1.1 | Types of studies While the original strategy did not set limits on the types of studies to be reviewed, the results of initial searching proved so prolific that it was decided, on the basis of quality, to focus on two main types of quantitative studies-RCTs and quasi-experimental studies (in which a control group was employed but allocation was not strictly randomized). The mixed methods strategy proposed initially in the protocol (Lietz et al., 2018) was thus replaced with a purely quantitative review and meta-analysis. Otherwise, this review followed the approaches to search strategies and analyses specified in the study protocol (Lietz et al., 2018) which was published by the Campbell Collaboration prior to starting the research.
The studies could occur in schools or out-of-school settings (e.g., home, larger community) or clinical settings, as long as the intervention was designed to improve outcomes in real-world settings.
The comparison groups used in the majority of included studies were waitlist control groups or standard treatment/treatment-asusual (TAU) groups. Two studies, namely vanSteensel_2015 1 and Ohan_2016, were included as pre-and posttest comparisons only. In vanSteensel_2015, the intended comparison group was children with an anxiety disorder but no ASD. Ohan_2016 combined their immediate treatment and waitlist groups after initial testing indicated that there was no significant change in the scores of the waitlist group, thereafter reporting pretreatment and posttreatment scores for the combined group. A third study, Pryor_2016, used a crossover design so only results collected after the first intervention round were used in the current analyses.

| Types of participants
The target population for the review is mainstream school-aged children, diagnosed with ASD (inclusive of autism, ASD, Autistic Disorder, Asperger's Disorder, Asperger Syndrome, atypical autism, PDD-NOS) by a professional eligible to diagnose these conditions, and also experiencing anxiety symptoms or a diagnosis of an anxiety disorder provided by a professional eligible to diagnose such conditions. The majority of included studies (21 of 24) used a screening instrument to confirm the existence of clinically significant levels of 1 Studies included in this review are cited by using first-author_date, rather than APA style. HILLMAN ET AL. | 5 of 35 anxiety at intake, while the remaining studies relied on parent or teacher reports of elevated anxiety.
If studies included a sample of children in the target population as well as other children (e.g., the general population) and the findings were separated for the ASD subgroup, the study was included in the review whereby the type of ASD diagnosed did not matter. In contrast, if the study findings were not reported separately (e.g., the results for children with ASD and ADHD were combined for analysis), the study was excluded from the review as the impact of the intervention on only the ASD sample would be impossible to isolate.
To be included in the review, either all participants in a study had to be of mainstream school age or a majority of participants had to be of mainstream school age. This meant that while most studies involved young people aged 6-16 years, one study (Piravej_2009) included some younger children (minimum 3 years old) and six studies included  The following is an example of study that was excluded due to it being a pharmacological only treatment: Other excluded studies are summarized in Table 1.

| Types of outcome measures
The primary outcome for included studies was anxiety, thus studies that focused on social skills interventions or other symptomatology of ASD as primary outcomes were excluded from this review. The measurement of anxiety (and related terms) had to be undertaken using valid and reliable approaches such as diagnostic interviews, screening instruments, observational ratings, and behavioral checklists-irrespective of the informant (e.g., student, parent, teacher).
Only the immediate posttreatment outcome is included in the current review, as the variety of follow-up schedules in the studies proved quite large, with 10 studies having no follow-up, 6 studies following-up less than 3 months after the end of the intervention, 4 studies after exactly 3 months, and 4 studies more than 3 months after the intervention (see Table 2). Compiling the results from different studies into ranges may have resulted in a loss of data integrity.

| Types of settings
The settings in which the intervention was applied were realworld settings such as school or home. While 19 of the interventions were conducted in a clinical setting (either a universitybased clinic or a community clinic, such as Child and Adolescent Mental Health), the intention of the studies was to address issues that were pertinent to the subjects' lives-either at home or in school.

| Search methods used for the identification of studies
Our search strategy identified published as well as unpublished literature, first, via electronically searching 12 bibliographic databases and, second, by searching additional gray literature sources such as selected websites, repositories, and research registers. We also manually searched targeted journals and reference lists and contacted key researchers in the field of autism to inquire about studies.
To ensure our search was as extensive as possible, we balanced our search strategy as far as was practical, toward a sensitive search rather than a precise search.
In summary, studies were included in the review if they met the following criteria:  3. At least one outcome measure was a standardized continuous measure of anxiety (parent, clinician, or self-reported).
4. The study was published between the years 1996 and 2018.

| Electronic searches
A broad range of bibliographic databases were electronically searched for studies that matched our inclusion criteria: • Academic Search Complete (via EBSCO) • A+ Education (via Informit) • British Education Index (via EBSCO) • CBCA Complete (via Proquest) • CINAHL (via EBSCO) • Education Research Complete (via EBSCO) • EMBASE (via Elsevier) • ERIC (via EBSCO) • PsycINFO (EBSCO) • PubMed • SCOPUS (via Elsevier) • TITLE-ABS-KEY((asperger* OR autis* OR asd OR "Pervasive Developmental" W/0 disorder* OR "PDD NOS" OR "PDD unspecified")) AND TITLE-ABS-KEY((anxiety OR anxious OR internali* OR fear)) AND TITLE-ABS-KEY ((student OR child* OR adolescen* OR preadolescen* OR (pre W/0 adolescen*) OR youth OR teen* OR (teen W/0 age*) OR "young people" OR "young person" OR boy OR girl)) AND TITLE-ABS-KEY((intervention OR treatment OR therap* OR psychotherap* OR evaluation OR outcome OR program* OR trial* OR experimental OR (control W/0 group) OR random* OR (best W/0 practi*) OR "evidence based"))) Research reviews: Wherever possible, the following search statement was executed in the list of resources below: (asperger OR autism OR autistic OR ASD OR "pervasive developmental" OR "PDD NOS") • Campbell Library • Cochrane Central Register of Controlled Trials (CENTRAL) • The JBI Database of Systematic Reviews and Implementation Reports.
• Database of Promoting Health Effectiveness Reviews (DoPHER) • Evidence for Policy and Practice Information and Coordinating Centre (EPPI-Centre) • Cochrane Database of Systematic Reviews • PROSPERO International prospective register of systematic reviews Where further refinement was necessary, we added additional search terms relating to the concept of anxiety. Alerts were manually scanned for any new references that fitted our search criteria.
Colleagues: Contact was also made with researchers and colleagues in the field and from the review's advisory group, to identify any additional studies, particularly those that might have been ongoing or unpublished at the time of our work.
Ongoing trials: We identified current and ongoing trials via the following trial registries:

• International Clinical Trials Registry Platform Search Portal
• Clinical Trials.Gov

• Trials Register of Promoting Health Interventions (TRoPHI)
• Cochrane Central Register of Controlled Trials -Cochrane Library We searched for the following terms: (Asperger OR autism OR autistic OR asd OR "pervasive developmental" OR "pdd nos") Where further refinement was required, we included anxiety and/or trials limited to children.

| Publication date range
Our searches were limited to a publication date range of 1996-2018.
We selected 1996 as the earliest publication date in order to narrow the scope of interventions to current approaches used in the last 20 years. Given the development of understanding in this field, we believe that interventions before this date would be less progressive in their approach. The initial database searches were conducted be-

| Other criteria
The searches in our selected sources were not restricted by geography, language, publication type, or by publication status. However, the selected sources are focused on the English language in keeping with our database subscriptions and the primary language of the authors.

| Selection of studies
As a first step in the screening process, four reviewers independently assessed titles and abstracts of a purposely heterogeneous subset of five studies identified through the searches. The purpose of this step was twofold: first, it determined their potential eligibility for inclusion in the review and second it served to develop a common understanding and application of inclusion criteria. Once a consensus regarding the application was reached, all abstracts were assessed by at least two reviewers. Where two reviewers disagreed regarding the inclusion of an abstract in the study, resolution was sought through discussion with the full project team. At the end of this step, studies that clearly did not meet the criteria, as well as duplicates, were removed.

| Data extraction and management
Full-text articles were then retrieved for the included abstracts.
Reviews of the full-text articles were undertaken independently by Discrepancies were checked and resolved. The data extracted included specific details about the interventions, populations, study methods, and outcomes of significance to the review question and specific objectives.

| Assessment of risk of bias in included studies
The risk of bias assessment was carried out by authors K. H. and K. D.
The assessment was informed by initial data extraction in JBI SU-MARI and conducted using the Cochrane Collaboration's guidelines for assessing risk of bias (Higgins, Altman, & Sterne, 2011). Risk of bias in the selected studies was rated as high risk (bias that potentially reduces the reliability of the results), or low risk (bias that is unlikely to alter the results), with an unclear category used in cases in which there was insufficient information in the published study for the judgment of bias to be made. As the majority of included studies were RCTs, the risk of bias assessment focused on methodological issues pertaining to this form of study-sequence generation, allocation concealment, blinding of participants and personnel, blinding HILLMAN ET AL.
| 15 of 35 of outcome assessment, attrition, selective reporting, and other sources of bias. As a consequence, the quasi-experimental studies that were included in this review received higher ratings of risk of bias, particularly in terms of selection bias.

| Measures of treatment effect
Only one outcome per respondent group was used in the quantitative syntheses to avoid double counting. In cases where there was more than one outcome measure per respondent available, we selected an outcome based on assessments of validity published in Wigham and McConachie (2014) and Lecavalier et al. (2014), the frequency of use across the included studies, and the availability of data appropriate for the meta-analyses.
Separate statistical analyses were conducted based on the informant for the outcome measures-namely parent, clinician, and self/student. While two of the included studies collected anxiety outcome measures from teachers of the subjects (Chalfant_2007; Luxford_2017), there were not enough teacher-informants to conduct a separate analysis. In addition, the extent of missing data for these measures was enough to raise concerns about reliability.
In accordance with the JBI SUMARI meta-synthesis program the SMD, reported as Cohen's d, and its 95% CI was used as the summary estimate of treatment effect size and based on the posttreatment/ wait-list scores reported in each study. This summary statistic was selected as all studies included continuous measures and all measures were in the same direction (i.e., higher scores indicating higher levels of behavior or impact of symptoms) and thus no adjustments were required. In addition to Cohen's d-although not available in the JBI SUMARI program at the time of analyses-Hedges' g is another method (i.e., formulae) commonly used for the computation of SMD.
Cohen's d and Hedges' g differ in that the latter uses the version of the standard deviation formula which divides by N-1, whereas the former divides by N. While, therefore, Hedge's g is often preferred for reviews involving studies with small sample sizes its use would not have led to different conclusions having been drawn from the results of the current review.

| Unit of analysis issues
Some of the included studies deviated from standard treatment versus control comparisons, in employing crossover designs (Pry-or_2016), inclusion of more than one treatment group (Sofron-off_2005) or inclusion of a control group without ASD who also received treatment (vanSteensal_2015).
For the crossover design, data from the baseline and the end of the first phase (prior to crossover) were used, effectively treating the alternative treatment group as a "TAU" control. Sofronoff_2005 included two treatment arms, one in which children received CBT on their own and another in which their parents participated in the treatment with them. While previous reviews have pooled the results of these two treatment arms (e.g., Kreslins et al., 2015;Ung et al., 2015), we elected to include them separately, as they do represent two different forms of intervention.
The study design of vanSteensal_2015 was relatively more complex, compared to other included studies, in that it included two treatment groups-one with ASD and anxiety disorders, one with anxiety disorders but no ASD diagnosis-and a wait-list control (WLC) subgroup of the ASD group. While the argument could have been made to exclude this study for a lack of formal diagnosis of ASD for those participants in the "anxiety disorders only" comparison group, it was decided to retain the study and focus on the immediate treatment versus WLC comparison within the ASD group.

| Assessment of heterogeneity
Quantitative data were, where possible, pooled by way of statistical meta-analysis. Weighted mean differences and their 95% CIs were calculated for analysis. Heterogeneity was assessed statistically using the standard χ 2 and also explored using subgroup analyses based on the different study designs included in this review.

| Assessment of reporting biases
Assessing risk of publication bias was an important task because of its potential influence on estimates of intervention effects. This review analyzed possible publication bias by implementing the trimand-fill method (Duval & Tweedie, 2000;Schwarzer, 2007), providing an initial assessment of whether unpublished data on ASD and anxiety interventions (likely to have null results) was evident (Uljarević & Hamilton, 2013).

| Data synthesis approach
Separate statistical analyses were carried out for clinician-reported, parent-reported, and self-reported outcome measures of anxiety.
Studies were also coded dichotomously for two possible moderator to be indicative of small, moderate, and large effects, respectively (Cohen, 1988). However, heeding concerns by Valentine and Cooper (2003) and Lipsey et al. (2012) that effect in the field of education are likely to be small and risk being overlooked if based on Cohen's interpretation, effect sizes were interpreted in an educational context using the metric developed by Higgins et al. (2013) for the UK Education Endowment Foundation. Accordingly, SMDs of 0.05, 0.19, 0.45, and 0.70 were taken to be indicative of low, moderate, high, and very high effects, respectively. Moreover, these can be interpreted, respectively as, 1 month, 3 months, 6 months, and 9 months additional developmental progress. A random effects meta-analysis was employed due to the variability in outcome measurement instruments and interventions across the included studies.
Using the JBI SUMARI meta-synthesis program, SMD (Cohen's d) estimates were calculated based on the posttreatment mean scores and standard deviations provided in each study. Since the direction of the scales was the same for all outcome measures, no adjustments of the scores were required. The statistical significance level was set at p < .05. Forest plots were used to illustrate results from individual studies. In the case of multiple treatment arms, such as Sofron-off_2005, the scores of both intervention groups (ITs) were compared to the control group score. Similarly, if a study reported more than one outcome measure for a respondent, then both outcomes have been reported, rather than presenting an average score as previous systematic reviews have done (e.g., Kreslins et al., 2015;Lang, Regester, Lauderdale, Ashbaugh, & Haring, 2010;Perihan et al., 2019;Sukhodolsky et al., 2013;Ung et al., 2015).  two were home-based interventions and two were school-based.

| Study design
Six of the studies were classified as quasi-experimental designs, in that they employed a control or comparison group that was not randomly assigned, while the remaining 18 studies used a randomized WLC design (with varying degrees of fidelity).    Vagg, & Jacobs, 1983); and the Social Worries Questionnaire (SWQ: Spence, 1995). A summary of some of the key elements of the included studies is presented in Table 2.

| Comparisons to previous reviews
Eight of the studies had not been included in previous reviews of interventions for anxiety in the ASD population, predominantly due to being published after the reviews were completed and because the current review also included theses and dissertations that were experimental or quasi-experimental studies. Table 3   noninclusion. As can be seen, the main reason for not including studies in this current review is their observational design.

| Excluded studies
As indicated in Figure 1, 95 of the full-text papers retrieved were excluded from the current review: 19 did not report levels of anxiety among participants, 16 had no outcome measure of anxiety, 15 did not employ a control or comparison group, 10 had a participant age range out of scope (and no potential for isolating participants within scope), 10 studies were classified as purely observational (pre-and postintervention in single group only), seven had no formal diagnosis of ASD in their participants, six were secondary or follow-up analyses of previous studies that focused on aspect outside of inclusion criteria, four did not include an intervention that met criteria, two were proposals or study protocols only (no results were presented), and another six did not provide sufficient information to satisfy the selection criteria or had other issues. As summarized below and detailed in Appendices B and C in the Supporting Information Material, these 95 excluded articles included those studies that might reasonably have been expected to be included, such as those included in previous reviews, but which did not meet the inclusion criteria of the current review: • No anxiety present in participants=> 19 studies Chalfant_2007 Note: Studies included in other systematic reviews are presented in bold font, while those studies not included in previous reviews are presented in normal font. McNally-Keehn_2013, and Piravej_2009. Despite being identified as randomized controlled trials, Chalfant_2007, Pryor_2016, and So-fronoff_2005 did not provide suf ficient information about randomization methods or procedures to assess potential bias.
It should be noted that four of the included studies were classified as quasi-experimental studies, in that they included a comparison group but that allocation to groups was not random. Of the quasi-experimental studies, Hepburn_2016 used a pair-wise matching scheme for allocation to groups, Ohan_2016 claimed that the order of enrollment "approximated" randomization, while Re-aven_2009 had subjects act as their own WLCs.
Allocation concealment was not detailed in the majority of studies, although Conaughton_2017 and Wood_2017 maintaining concealment by conducting baseline measures prior to randomization, and McConachie_2014, Murphy_2017, and Storch_2015 by concealing treatment group allocation from the researchers and independent evaluators throughout the studies.

| Performance and detection bias
Performance bias was universally high, due to the nature of the interventions, as it was not possible to blind participants from their treatment group allocation.
Detection bias was higher among studies that used outcome measures based on the reports of participants themselves or their parents (many of whom had also participated in family-based interventions), but lower in studies that used reports from clinicians or teachers who were blinded to IT allocation. For those studies that used multiple outcome measures from different informants, the risk of performance bias was rated for each outcome measure separately.

| Attrition bias
Attrition was rated as low in studies that had little to no attrition in subjects, who evaluated the effect of attrition by comparing therapy completer analyses with "Intent to Treat" analyses (i.e., analyses using original samples and data imputation techniques), or who compared the profile of study dropouts with completers with no statistically significant differences found. Attrition bias was fairly low across the studies, with only Ohan_2016 and Reaven_12 being rated as high. Ohan_2006 reported that six of the treatment families failed to complete their treatment (a loss of 25% of their sample), while Reaven_12 reported a treatment-completer sample of 47, but only provided baseline data for 43 participants (IT = 20 and TAU = 23) and used "last observation carried forward" imputation for missing data.

| Reporting bias
There was no evidence or suggestion of reporting bias in any of the studies. However, a risk of bias assessment was undertaken by rating each study as high, unclear, or low risk of bias against five attributes.
A summary of the risk of bias assessment for the included studies is presented alongside each forest-plot. In addition, publication bias was assessed using a funnel plot.
6.3 | Synthesis of results

| Treatment efficacy
Twenty-four studies reported outcome measures from one or more informants (clinicians, parents, student self-reports), with T A B L E 4 Studies that were not included in this review but were included in Perihan et al. (2019) Studies n Reasons for exclusion Drmic, Aljunied, and Reaven (2017) 44 Observational study Ehrenreich-May et al. (2014) 20 The BIACA intervention was already covered under the Storch 2015 paper (RCT study) for a larger age group (11 to 16 years); Also, no control group Maskey, Lowry, Rodgers, McConachie, and Parr (2014) 9 Observational study Ooi et al. (2008) 6 Observational study (pre-post design only, no control group) Scarpa and Reyes (2011) 11 No concurrent diagnosis of anxiety problems and no appropriate measure of anxiety as an outcome Thomson, Burnham Riosa, and Weiss (2015) 13 Observational (no control group) Weiss, Viecili, and Bohr (2014) 18 Observational study 60 informant reports in total, along with several teacher reports (see Table 2). These studies involved 1,020 participants (

| Moderator analysis
Also of interest in this study, was the potential moderating effects of a) family involvement in sessions and b) the individual or group nature of sessions. These two moderators were analyzed to help address the lack of similar investigations in previous reviews published, and to draw comparison to the most recent review by Perihan et al. (2019), which did consider the potential moderator of parental involvement.

| Family involvement
Two groups were created based on family involvement, in order to compare the outcomes of treatments with parental involvement (n = 15, excluding outlier Chalfant_2007) to treatments without parental

| Individual or group treatment
In order to compare the potential moderating effect of treatment format, two groups of studies were formed and assessed based on whether the treatment was administered on an individual basis (n = 9), like the Thai massage (Piravej et al., 2009), or in a group setting (n = 14), such as the peer-mediated, theater-based intervention (Corbett et al., 2017). The forest plot presented in Figure  Treatments that were administered individually one-on-one (SMD = −1.24, p < .01), indicated larger effects than for treatments delivered at a group-level (SMD = −0.37, p < .01).

| Overall completeness and applicability of evidence
The large number of studies meeting our original inclusion criteria was of sufficient size to warrant restricting the results to a metaanalysis of RCTs and quasi-experimental studies. Data on the primary outcome-anxiety-was gathered using a variety of instruments. Although this may be seen as a source of variability and imprecision in the results, all of the instruments used adhered to published recommendations for reliability and quality (Lecavalier et al., 2014;Wigham & McConachie, 2014) and have been analyzed in previous reviews (Kreslins et al., 2015).

| Quality of the evidence
The quality of the evidence can be considered moderate. Results in favor of treatment groups compared to control groups were fairly consistent across the included studies, although a number noted mixed nonsignificant results when using reports from more than one respondent (particularly, when using parent and self-reports).
Overall, the number of low and questionable assessments of risk outweighed those of high risk. There are, however, issues around the variety of outcome measures and informants that may introduce imprecision to the overall measures of effectiveness and thus should be considered.
The effectiveness of the interventions was generally stronger for clinician (mostly blinded) reports but lower among parent and self-report measures. Issues with self-report in ASD children have been noted in other reviews, with both Kreslins et al. (2015) and Sukhodolsky et al. (2013) reporting lower effect sizes when using self-report as the outcome measure of anxiety. It is difficult to identify whether these differences emerge from difficulties in interpreting the questions on the outcome measures or may reflect a lower level of insight into their own symptoms in this particular population. It is worth noting that none of the self-report outcomes measures had been designed, modified or normed for use with children with ASD.
Due to the nature of the interventions and the selected outcome measures, the risk of performance and detection bias were higher for some outcome measures (parent and self-reports) compared to others. Apart from Clarke_2017, which was a school-based intervention and included a parent report as an outcome measure, parents were aware of the treatment group their child was assigned to. Accordingly, the nature of the F I G U R E 7 Forest plot comparing treatments with and without family involvement interventions made it impossible to blind participants themselves to treatment status, so all self-reports may reflect high performance and detection bias. Given this high risk of bias, the results, particularly those based on parent or self-report should be interpreted with caution.

| Limitations and potential biases in the review process
Although the systematic nature of the review process followed here, decreases the potential for bias, risks of bias in the review process remain. The greatest risk of bias of this review was the selection of studies, specifically, the decision to limit the inclusion criteria to randomized control studies and quasi-experimental studies. The inclusion of RCTs alongside quasi-experimental studies, and studies of CBT alongside other interventions, may have introduced variability to the estimates of effectiveness and is thus a potential limitation to the results.

| Agreements and disagreements with other studies or reviews
The results of this review and meta-analysis suggest there is moderately strong evidence for the effectiveness of psychosocial interventions, such as CBT, in reducing anxiety amongst mainstream school-aged children with ASD. This is consistent with the conclusions of similar reviews (Kreslins et al., 2015;Sukhodolsky et al., 2013;Ung et al., 2015), although these reviews focused solely on CBT, while this review included other approaches.
The results of the current review do differ from previous reviews, however, in finding that the interventions were effective even from the point of view of the children participating in them. This meta-analysis found an SMD of −0.35, p = .001, when using selfreport as the outcome measure, compared to d = −0.65 (p = .10) in Kreslins et al. (2015) and d = −0.68 (p = .12) in Sukhodolsky et al. Evidence in support of other psychoeducational interventions, such as massage and theater therapy to address social anxiety, is more limited, not just due to the popularity of CBT but also due to the quality of the smaller number of non-CBT studies available.
While the review does indicate that interventions based on the principles of CBT may be effective for reducing anxiety, the variety of curricula (and modifications made to those curricula) used in the studies included may have confounded the results. There were not a sufficient number of studies that employed the same curricula (even those that used the same base curricula may have made different modifications) to allow for a direct comparison of effects between curricula, and so it is not possible to provide recommendations as to whether one CBT curricula might be more effective than another, or indeed whether any one program may be more effective with a certain subgroup of participants (e.g., individuals with an intellectual disability, ADHD). However, as CBT provides an overarching theoretical framework upon which curricula are based, different programs that are grounded in the principles of CBT should, at least in principle, have similar degrees of effectiveness.

| Implications for research
The results of this review suggest that while there is evidence that CBT is an effective behavioral treatment for anxiety in some children and youth with ASD, there is still work to be done in terms of identifying the characteristics of these interventions that contribute to their effectiveness and identifying the characteristics of participants who are more likely to respond to such interventions. The results suggest that group therapies are less effective than individual one-on-one therapies and that having the family involved is more effect at reducing anxiety than not. Many of the studies reviewed here included modifications to published curricula that were hypothesized to improve the acceptance and effectiveness of the interventions for children with ASD, such as visual aids, highly structured sessions and flexibility around the number of length of sessions. It is unclear what effect, if any, the use of different curricula and modifications had on the results of this review. Future research with larger samples and active control groups are necessary to allow direct comparisons of the different curricula and identification of the characteristics of participants (e.g., age, social competence, level of language ability, and communication skills) for whom the intervention is most likely to be of benefit.
Research should also focus on expanding the cognitive functioning levels of participants (i.e., including individuals with below average cognitive abilities) so as to identify the characteristics of interventions that can be employed with children and adolescents with ASD and lower levels of general functioning or language ability.
The trend of somewhat weaker effects of interventions when outcomes are measured via self-report, noted here and in similar reviews (e.g., Kreslins et al., 2015;Sukhodolsky et al., 2013) warrants further investigation. It may be that this trend reflects actual differences in the perceived benefits of interventions between clinicians, parents and children. However, it is troubling to assume that the more valid assessment of a child's experience is an external observer, whether that be a clinician or a parent. Other factors, such as the development of self-awareness and understanding of health concepts, have been suggested by other researchers as potential sources of inconsistency in self-reports with children, and more particularly with children with ASD (Kreslins et al., 2015).
Some suggest that individuals with ASD can manifest in ways that are idiosyncratic and not aligned with the ways that anxiety presents in non-ASD populations (Kerns & Kendall, 2012;Uljarević et al., 2018). Certain traits and behaviors, such as social avoidance or rigid, ritualistic behaviors, can be a manifestation of both core ASD symptomatology and indicative of comorbid anxiety (Kerns et al., 2015). However, with rare exception (see Rodgers et al., 2016), instruments used to measure anxiety in ASD have been develop for non-ASD populations. Such instruments are not designed to be sensitive to distinguishing atypical anxiety presentations in ASD populations nor distinguish whether a particular symptom is a presentation of ASD or comorbid anxiety-nor should they be. Nevertheless, current instruments might at the same time both over-and undersample anxiety problems associated with ASD.
What may be of importance, however, is whether symptoms are more or less responsive to intervention among populations with anxiety alone versus those with ASD and comorbid anxiety, which might be more ingrained. Accordingly, the development of instruments for anxiety symptoms that are specifically designed for and normed with ASD population may be of use.
It may be worth considering the input of those with ASD in the design and modifications of interventions for anxiety. As with other groups, it is important to involve people with ASD in the design and modification of interventions designed for them, including those targeting anxiety. People with ASD are likely to be able to shed important insight into the strengths and weaknesses of different approaches, and also to the specific skills required of therapists working with this population. Finally, it is imperative to develop instruments that are valid in assessing treatment effects in people