Much research on anxiety in ASD and OCD has relied on measures developed and validated in non-ASD populations. The ability of these measures to accurately capture the constructs of anxiety and OCD in individuals with ASD is under investigation (Grondhuis & Aman, 2012; Kerns & Kendall, 2012; van Steensel et al., 2011). Research has begun to explore the psychometric properties of current anxiety and OCD measures in ASD samples and, further, to adapt these measures to better differentiate and capture overlapping and atypical symptoms. This section will review the pros and cons of a selection of anxiety and OCD measures that have received the most empirical attention for individuals with ASD. To cover a broad range of clinical assessment needs, we review measures designed for brief and comprehensive assessment, screening and diagnosis, broad anxiety symptoms and specific diagnoses, as well as measures suitable for a varied range of ages and intellectual ability (see also: Grondhuis & Aman, 2012; Lecavalier et al., 2014; Wigham & McConachie, 2014).

A number of informant and self-report measures of child behavior have been utilized and assessed in youth with ASD. These include general measures of psychopathology with anxiety subscales and anxiety-specific scales. Because these measures are brief, continuous in nature, and completed by youth and their caregivers, they can—when reliable and valid—provide a quicker, more efficient means to screen for anxiety problems or track symptom change over time. Below we summarize research on the reliability and validity of various anxiety questionnaires in youth with ASD.

Research on the assessment of anxiety in individuals with ID, with and without ASD, has lagged behind that of individuals without intellectual deficits (Hagopian & Jennett, 2008). The Autism Spectrum Disorders—Comorbidity for Children (ASD-CC ; Matson, LoVullo, et al., 2009) is a 39-item informant-rated anxiety scale designed to assess anxiety in youth (ages 2–16 years) with ASD and varied intellectual functioning. The ASD-CC Worry/Depressed subscale has shown convergent and discriminant validity with similar and dissimilar subscales of the BASC-2 (Rieske et al., 2013), but its retest reliability, sensitivity, and specificity have yet to be evaluated. In addition, the Anxiety Depression and Mood Scale (ADAMS ; Esbensen, Rojahn, Aman, & Ruedrich, 2003) is a 28-item informant-rated scale of behaviorally based mood and anxiety symptoms that has shown promising psychometrics in youth with ID. Though untested in individuals with ASD, the ADAMS is a potentially appropriate measure for this group given its brief nature and behavioral emphasis. Finally, the Baby Infant Screen for Children with aUtIsm Traits—Part 2 (BISCUIT ; Matson, Fodstad, & Mahan, 2009), Diagnostic Assessment for the Severely Handicapped-II (DASH-II ; Matson, 1995), Psychopathology in Autism Checklist (PAC ; Helverschou, Bakken, & Martinsen, 2009), and Developmental Behavior Checklist (DBC ; Einfeld & Tonge, 1995) have been used in some studies to assess anxiety problems in youth with ASD and ID (e.g., Bakken et al., 2010; Bradley, Summers, Wood, & Bryson, 2004; Brereton, Tonge, & Einfeld, 2006; Helverschou & Martinsen, 2011). All are informant ratings designed to assess a range of behavior problems that include anxiety subscales. Such measures may be most helpful for screening or early stages of assessment, and they should be followed by a more comprehensive interview with multiple informants and behavioral observation of the individual.

Very few studies have focused on the assessment of anxiety problems in adults with ASD. Matson and Boisjoli (2008) evaluated the psychometrics of the Autism Spectrum Disorders—Comorbidity for Adults (ASD-CA ) measure, an informant scale to assess comorbid psychopathology in adults with ASD and ID. The ASD-CA items and factors demonstrated variable inter-rater reliability (0.07–0.77) and internal consistency (0.44–0.91); however, results of the exploratory factor analysis were promising and the overall internal consistency for the scale was good (0.91). The 21-item Beck Anxiety Inventory (BAI; Beck & Steer, 1993) has also been found to be a reliable tool for assessing anxiety in adults with and without intellectual disability (Lindsay & Skene, 2007). The BAI has been used to assess anxiety in adults with ASD in several studies, though psychometric data is lacking (Cath, Ran, Smit, van Balkom, & Comijs, 2008; Lai et al., 2011). Similarly, the Liebowitz Social Anxiety Scale (LSAS ; Heimberg et al., 1999), a 24-item self-report of social anxiety symptoms, has been used to assess social anxiety in cognitively able adults with ASD in some studies with good internal consistency (Cath et al., 2008; Dziobek, Gold, Wolf, & Convit, 2007; Kanai et al., 2011). Further research on its reliability and validity in ASD samples is needed.

Research suggests that there is both considerable overlap and also variability in the presentation of anxiety and OCD in people with and without ASD (Kerns & Kendall, 2012; Ozsivadjian, Knott, & Magiati, 2012; White, Lerner, et al., 2015). As such, existing anxiety and OCD measures have much to offer clinicians and researchers, and also considerable room for improvement. ASD-specific adaptations are needed and emerging (Kerns et al., 2014; Kuusikko et al., 2008; Leyfer et al., 2006; Sukhodolsky et al., 2008), but may limit comparisons across individuals with and without ASD (van Steensel et al., 2011). Specifically, comparisons across studies and samples may be complicated by methodological differences (i.e., use of different tools) and conceptual differences (i.e., discrepancies in how anxiety is conceptualized). In general, it is highly recommended that researchers and clinicians use multiple methods, including expert clinical judgment, direct observation, and multiple informants to accurately assess anxiety and OCD in ASD. Given that rating scales often yield higher than expected scores for people with ASD, clinicians must be cautious about interpreting scores (which may be elevated due to other difficulties associated with ASD) and should not rely on a single indicator. Multi-informant assessment may be particularly important when parent-youth reports tend to be discrepant, as in youth with ASD (e.g., Gillott et al., 2001; Russell & Sofronoff, 2005; White et al., 2012). This type of multifaceted approach will improve understanding of the constructs of anxiety and OCD in ASD, as well as the strengths and weaknesses of various individual measures.

Determining whether psychiatric symptoms in individuals with ASD are part of core ASD features or whether they represent anxiety is a complex clinical issue. This section highlights key points for differential and dual diagnostic decision-making, in hopes of aiding the accurate identification of co-occurring anxiety disorders. Before providing recommendations for each anxiety disorder separately, several general guidelines are offered here.

Anxiety symptoms can be conceptualized along three dimensions: physiological, behavioral, and cognitive (Lang, 1968). Physiological symptoms include signs of arousal, such as tachycardia (i.e., quickened heart rate), blushing, trembling, and sweating, along with somatic complaints (e.g., nausea, headaches, muscle tension). The primary behavioral symptom of anxiety is avoidance of feared stimuli and situations. Behavioral avoidance may be obvious (e.g., running away from a bee) or more subtle (e.g., avoiding eye contact). Hypervigilance and checking are also common behavioral symptoms. Cognitive symptoms typically include catastrophic predictions and other negative thoughts. This model of anxiety provides a framework to determine whether an assessment battery covers all three domains. Given that ASD and anxiety share common features, it can be helpful to use this framework to organize an individual’s different symptoms and determine whether an ASD diagnosis accounts for all presenting problems, or whether there is support across the three dimensions of anxiety to diagnose an anxiety disorder.

The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5 ; APA, 2013) highlights how anxiety and fear may manifest differently in children (e.g., fear or anxiety may be expressed by crying, tantrums, freezing, or clinging). We encourage clinicians to think similarly about individuals with ASD of all ages—they may self-report and/or manifest anxiety symptoms in a different way than do individuals without ASD. For example, people with ASD may make vague statements about having “bad feelings” instead of “feeling anxious” (Kreiser & White, 2014). Based on a focus group with parents of youth with ASD, Ozsivadjian and colleagues (2012) identified five common categories for the ways that anxiety is expressed in this population: (1) challenging behaviors (e.g., tantrums), (2) avoidance or escape, (3) hyperactivity or heightened arousal, (4) increased sensory behaviors, and (5) increased repetitive behaviors. These categories highlight how, relative to typically developing individuals, anxiety in people with ASD can present similarly (e.g., avoidance, increased arousal) or differently (e.g., aggression), often amplifying the core ASD deficits (e.g., sensory or repetitive behaviors).

Diagnostic decisions are even more challenging without direct verbal expression from the individual. When assessing individuals with limited expressive language, clinicians must rely more on their assessment of behavioral and physiological symptoms of anxiety. One way to directly observe behavioral and physiological reactions to a feared stimulus is a behavioral avoidance test (BAT), an individualized task that involves gradually exposing a person to his or her feared stimulus to assess when avoidance and/or anxiety is displayed (Dadds, Rapee, & Barrett, 1994). BAT participants may also indicate their subjective experience of fear with Subjective Units of Distress Scale (SUDS ) ratings and visual aids.

In order to constitute comorbidity of any anxiety disorder with ASD, the following should be established:

To provide more specific recommendations for distinguishing co-occurring anxiety symptoms from core ASD symptoms, the assessment of each anxiety disorder is described below. This information is based on the DSM-5 (APA, 2013), which takes a developmental lifespan perspective and presents anxiety disorders chronologically according to their average age of onset. As will be clear from this section, we currently know more about certain anxiety disorders in the context of ASD (e.g., Social Anxiety Disorder) than others (e.g., Panic Disorder, Agoraphobia).