Circumscribed interests in autism: are there sex differences?

Sallie Wallace Nowell (Frank Porter Graham Child Development Institute, The University of North Carolina at Chapel Hill, Carrboro, North Carolina, USA)
Desiree R. Jones (School of Behavioral and Brain Sciences, The University of Texas at Dallas, Richardson, Texas, USA)
Clare Harrop (Department of Allied Health Sciences, The University of North Carolina at Chapel Hill, Carrboro, North Carolina, USA)

Advances in Autism

ISSN: 2056-3868

Article publication date: 20 February 2019

Issue publication date: 11 June 2019

Abstract

Purpose

Sex differences in circumscribed interests (CI) may delay diagnosis for females with autism spectrum disorder (ASD); therefore, it is important to characterize sex differences in CI to determine if differential approaches to diagnostic assessment are warranted for females with ASD. The purpose of this paper is to examine sex differences in parent-reported quantity, content and functional impairment of children’s interests.

Design/methodology/approach

Parent responses to the Interests Scale were analyzed using descriptive statistics and ANOVAs to determine diagnostic (ASD vs typical development (TD)) and sex differences between four groups of children ages six to ten years: ASD males, ASD females, TD males and TD females.

Findings

Groups were comparable on the quantity of interests reported on the Interests Scale. Children with ASD demonstrated significantly more nonsocial interests and had greater functional impairment associated with their interests than TD children. A significant diagnosis×sex effect was found for the number of interests in folk psychology. Descriptively, males with ASD were more likely to have a primary interest in the traditionally male category of physics than females with ASD whose primary interest mainly fell into the categories of TV or the more traditionally female category of psychology.

Originality/value

These findings strengthen the results of Turner-Brown et al. (2011) by replicating their findings that children with ASD have more nonsocial interests and greater functional impairments related to their interests compared to TD children in a sample that is balanced on biological sex. However, there are distinctions between males and females with ASD in their primary interests that have implications for diagnostic assessment.

Keywords

Citation

Nowell, S.W., Jones, D.R. and Harrop, C. (2019), "Circumscribed interests in autism: are there sex differences?", Advances in Autism, Vol. 5 No. 3, pp. 187-198. https://doi.org/10.1108/AIA-09-2018-0032

Publisher

:

Emerald Publishing Limited

Copyright © 2019, Emerald Publishing Limited


Introduction

Restricted and repetitive behavior (RRB) is a core symptom domain of autism spectrum disorder (ASD) as defined by the Diagnostic and Statistical Manual of Mental Disorders – 5th ed. (APA, 2013). Two types of RRBs have been described in the literature: higher and lower order (Turner, 1999). Lower order RRBs include motor actions and movements. These RRBs have been more commonly observed in individuals with developmental delay or intellectual disability (Barrett et al., 2004; Lam et al., 2008). Higher order RRBs include more advanced cognitive behaviors such as insistence on sameness, need for routines and circumscribed interests (CI) (Szatmari et al., 2006; Turner, 1999). Compared to other types of RRBs, higher order RRBs, specifically CI, appear to be unique to individuals with ASD; thus, it is important to characterize CI in individuals with ASD and their potential impact on learning and social outcomes.

CI are defined as intense preoccupation with one subject or a narrow range of subjects. Approximately 75–88 percent of children with ASD have one or multiple CI (Klin et al., 2007; Lam et al., 2008; Smith et al., 2009). Though the content and focus of CI often include interests shared by typical development (TD) peers (e.g. vehicles, animals, electronics; DeLoache et al., 2007), CI in ASD have been described as more nonsocial, less age-appropriate, less functional (Turner-Brown et al., 2011) and more idiosyncratic (Mercier et al., 2000; South et al., 2005) than the interests of TD peers. Because individuals with ASD are often inflexible about the ways they will engage with their CI, preoccupation with CI may limit the quantity and quality of social experiences necessary for cognitive and social development in children with ASD and thus lead to functional impairments (Turner-Brown et al., 2011).

It should be noted that CI are not always a weakness requiring intervention; in fact, use of a CI to individualize learning materials may increase participation in new activities and social engagement (Maled et al., 2007; Dunst et al., 2011). CI can also serve as areas of strength and benefit leading to opportunities for social engagement with others (Mercier et al., 2000). In some cases, CI allow the individual to develop specialized skills and abilities that may benefit society and lead to employment opportunities (Patten Koenig and Hough Williams, 2017). Finally, just as hobbies and interests in typical development do, CI provide pleasure to individuals with ASD (Sasson et al., 2012).

Biological sex and circumscribed interests

ASD affects more males than females, with a ratio of 3 to 4 males diagnosed to each female (Brugha et al., 2011; Chakrabarti and Fombonne, 2005; Baio et al., 2018). Less is known about females diagnosed with ASD as the majority of reported research findings, as well as assessment and treatment practices in ASD are based on largely male samples.

However, females with ASD demonstrate differences in their ASD symptoms compared to males that may differentially affect their developmental trajectories. In a mixed methods study of 46 adolescents in special education (half with ASD), females with ASD (n=13) demonstrated higher social motivation on the teacher-rated Social Responsiveness Scale 2 (Constantino and Gruber, 2012) and in semi-structured interviews than ASD males (Sedgewick et al., 2016). Females with ASD have also been shown to demonstrate friendship behaviors that are more similar to peers compared to males with ASD (Dean et al., 2014, 2017; Head et al., 2014). Using adapted versions of the Friendship Quotient (FQ; Baron-Cohen and Wheelwright, 2003) completed by both children and their parents, Head et al. (2014) found that though ASD males and females reported fewer friendship behaviors than TD males and females, females with ASD (n=25) reported friendship behaviors most similar to TD male peers. The child version of the FQ used in this study had weak internal consistency, so results should be interpreted with caution. Similarly, Dean et al. (2017) used mixed methods to compare the social environments of girls and boys with ASD. In a natural school playground environment, girls with ASD (n=24) were observed to jointly engage with other children by chatting and flitting between activities, much like their TD female peers. They also demonstrated some solitary play like ASD males; however, they did this in closer proximity to other children such that their social challenges were more difficult to detect than those of ASD males (Dean et al., 2017).

Differences in higher order RRBs and CI have emerged as another potential distinction between the sexes. Lower rates of RRBs have been reported in females with ASD as compared to males (Szatmari et al., 2012), particularly those classed as higher order (Frazier et al., 2014), and the interests of females with ASD have been described as more aligned with those of their peers with typical development (Hiller et al., 2014; Sutherland et al., 2017). In a sample of students with ASD who had average cognitive abilities, Hiller et al. (2014) found that females with ASD (n=69) were ten times less likely to meet DSM-5 criteria for RRBs compared to males with ASD and their interests were more random (e.g. rocks, stickers). Using a survey of parents of children with ASD, Sutherland et al. (2017) reported that parents of ASD females (n=171) had interests that were more gender typical than those of ASD males; however, they did not have a TD female control group with which to compare these parent reports. Using observations of play, Harrop et al. (2017) found that toy choices aligned more closely between females with and without a diagnosis of ASD than with males with ASD. Specifically, preschool-aged females with ASD played with toys that are typically classified as female. These findings have been extended using eye-tracking methods. In two recent studies, Harrop et al. found that females with ASD attended to images of female interests (such as dolls, tea sets and characters popular with girls; Harrop et al., 2018b) and also attended more to faces when these were paired with images of objects related to common, but perhaps male-biased, CI (Harrop et al., 2018a).

These sex differences may contribute to a milder presentation or serve as a “protective effect,” an aspect of being female that protects them from having symptoms of ASD (Robinson et al., 2013). Evidence for a protective effect has been found in twin studies (e.g. Robinson et al., 2013), but a specific genetic locus has not yet been found (Gockley et al., 2015). Females with ASD have reported that they have the ability to purposely “mask” or “camouflage” their social challenges by copying others, taking on a different persona or joking about their differences to better “fit in” with during social situations such that their ASD symptoms are not detected by others (Bargiela et al., 2016).

Sex differences may also delay diagnosis or lead to misdiagnosis for females on the spectrum. Research has found that for females to receive a diagnosis of ASD, they require greater symptom severity, more behavior problems or comorbid intellectual disability compared to males, potentially delaying their diagnosis and reducing opportunities for early intervention services (Banach et al., 2009; Dworzynski et al., 2012). Therefore, it is important to characterize sex differences in CI to determine if differential approaches to assessment and intervention are warranted for females and males with ASD. This study aims to add to this literature by replicating a study of parent-reported CI by Turner-Brown et al. (2011) and extending these methods to examine sex differences in the quality, content and functional impairment associated with children’s interests.

Turner-Brown et al. (2011) sought to characterize the CI of 50 school-aged children with ASD compared to age- and gender-matched TD children. Using the Interests Scale (Bodfish, 2003), they found no significant differences in the number of interests reported by parents, but the content and functional impairment of interests were significantly different by diagnostic group. The ASD group demonstrated significantly more interests in “folk physics” (e.g. mechanical systems, building, computers) than the TD group. Though both groups tended to play alone, the parents of TD children reported significantly more interest in play with peers compared to the group with ASD. Regarding functional impairment, parents of children with ASD reported significantly greater frequency of activities related to the interest, amount of interference of that interest with other activities, degree of resistance when interrupted and amount of accommodation required. They also reported significantly less flexibility and interest in inclusion of others compared to TD children. This sample was 95 percent male and, therefore, underpowered to detect sex differences.

This study aims to replicate and extend the findings of Turner-Brown et al. (2011) in order to address the following research questions:

RQ1.

Are previous findings that school-aged children with ASD demonstrate differences in parent-reported content and functional impairment of their interests, but not quantity of interests, compared to children without ASD replicable?

RQ2.

Are there sex differences in parent-reported quantity, content and functional impairment of children’s interests in ASD?

Based on the existing literature about females with ASD, we hypothesize that females with ASD will have interests that are more similar to those of their female TD peers with milder functional impairment than males with ASD, and therefore, we will find significant sex differences in the content and functional impairment of children’s CI.

Method

Participants were recruited into four groups based on biological sex and diagnosis: 27 ASD males; 27 ASD females; 16 TD males and 17 TD females. All children were aged between six and ten years due to recent literature reporting that, under age six, there are minimal sex differences in core ASD symptoms including CI (Harrop et al., 2015; Van Wijngaarden-Cremers et al., 2014). Children were excluded if they had a seizure disorder, acute mental condition or a genetic disorder, such as fragile X syndrome.

TD children were recruited from multiple sources: an e-mail sent to the Child Development Research Registry at (The University of North Carolina at Chapel Hill), social media posts and word-of-mouth. Exclusion criteria for TD children included diagnosis of a neurodevelopmental disorder or an immediate relative with a diagnosis of ASD. Parents were asked to complete the Social Communication Questionnaire (SCQ; Rutter, Bailey and Lord, 2003) to ensure that children did not demonstrate elevated symptoms of ASD.

Participants with ASD were recruited from the Autism Research Registry at (The University of North Carolina at Chapel Hill). Registry inclusion requires a Diagnostic and Statistical Manual of Mental Disorders (APA, 2013) diagnosis of ASD made by a licensed clinician with expertise in ASD, based upon both parent report and one or more standardized autism diagnostic assessments (e.g. Autism Diagnostic Observation Schedule (Lord et al., 2000) and Autism Diagnostic Interview – Revised (Rutter, Le Couteur and Lord, 2003). Diagnosis of ASD was confirmed via phone screening and completion of the SCQ (Rutter, Bailey and Lord, 2003) at study entry.

Procedures

All study assessments occurred at (The Carolina Institute for Developmental Disabilities lab space at the University of North Carolina at Chapel Hill). Children completed the Differential Abilities Scales (DAS-2; Elliot, 2007) with an examiner while parents filled out parent-report measures in the same room. Either before or after the DAS-2 was administered, children participated in a series of eye-tracking paradigms lasting about 30 min. Results from the eye-tracking portion of the study are reported elsewhere (Harrop et al., 2018a, b). This study met ethical standards for human subjects research and was approved by the Institutional Review Board at (The University of North Carolina at Chapel Hill). Informed parental permission and consent was obtained from study parents. If children were seven years of age or older, they assented to their own study participation.

Due to the challenges associated with recruiting a large enough sample of females with ASD for the study to be sufficiently powered, groups were not matched on mental age; however, there were no significant differences between diagnostic groups on mental age (see Table I). Males in this sample did have significantly higher mental ages on the DAS-2 than females F(1, 79)=4.33, p⩽0.04. The sample of TD children was significantly younger chronologically than the sample of children with ASD. As expected, children with ASD had significantly greater symptoms of ASD reported on the SCQ (Rutter, Bailey and Lord, 2003; F(3, 82)=42.83, p⩽0.01) and significantly more RRBs reported on the Repetitive Behavior Scales – Revised (RBS-R) compared to TD children (F(3, 85)=21.88, p⩽0.01). There were no significant sex differences found on the RBS-R or SCQ total scores. Chronological age was included in the models as a covariate in all analyses to control for the significant age difference between the TD and ASD groups.

Measures

The Interests Scale (Bodfish, 2003) is a parent-report measure of children’s CI. First, parents indicate whether or not their child is currently or has ever been interested in 39 common categories of interests (e.g. insects, arts/crafts, television/movies, people, collecting things, sports; for complete list of categories see Bodfish, 2003). The sum of these interests yields a total score of current and past interests for the child (score range 0–39). The second part of the Interests Scale asks parents to write down their child’s primary interest over the past month and answer seven questions about the amount of functional impairment associated with their child’s primary interest: overall degree of interest, frequency of specific activity related to interest, degree of interference with other activities, degree of resistance when interrupted, degree of flexibility/adaptability, amount of accommodation required and degree of solitary play around this interest. Items were summed to create a “total intensity rating” with higher ratings indicating a greater degree of functional impairment. Higher ratings on these items indicate greater severity of functional impairment and increased isolation (score range 2–23).

Coding and subcategorization of content of interests

Subcategories for folk physics and folk psychology were created from the Interests Scale based on the finding that children with ASD show more interests in folk physics and fewer interests in folk psychology than children with Tourette syndrome (Baron-Cohen and Wheelwright, 1999) and TD children (Turner-Brown et al., 2011). We used the same subcategories from the Interests Scale developed by Turner-Brown et al. (2011) for our analyses. The folk psychology subcategory was created by summing interests in people, religion, politics/government, social games and psychology. The folk physics subcategory was comprised of interests in machines, mechanical systems, physics, transportation, building, computers and object motions. Parents also reported their child’s interest in playing games with others (e.g. card games, board games, multi-player video games) and playing games alone (e.g. single-player video games, handheld personal game systems, one-person card or board games) on the Interests Scale.

Each child’s primary current interest, as reported by parents, was categorized into one of thirteen interest areas based on Baron-Cohen and Wheelwright (1999). Two of the authors independently categorized each interest with 93 percent agreement. Consensus was reached for the interests for which the authors disagreed.

The DAS-2 (Elliot, 2007) is a measure of cognitive ability for children ages 30 months to 17 years, 11 months. The core battery of six subscales was administered to all children in the study. The majority of children were able to complete the school years form, but four children with ASD and one with TD completed the early years protocol. Core subscale scores are comparable across the test forms. Age equivalents were derived to give an estimate of mental age for each participant (see Table I).

The RBS-R (Bodfish et al., 1999) was completed by parents as a measure of RRBs in the sample. The RBS-R has 43 parent-reported behavior ratings ranging on a four-point Likert scale from “0” does not occur to “3” occurs frequently and/or is severe. Parents are asked to consider the frequency of the behavior, how challenging it is to interrupt and the degree of interference with everyday life caused by the behavior in their responses. The RBS-R yields six subscale scores and the sum of these subscales comprises the total score (see Table I).

The SCQ (Rutter, Bailey and Lord, 2003) is a parent-report of overall autism symptomology. It was completed by parents of both children with ASD and TD to confirm eligibility for the study.

Results

All statistical analyses for this study were conducted using JMP Pro version 13.2.1 (SAS Institute, 1989–2016).

Psychometric properties of the interests scale

Internal consistency of the Interests Scale was examined for this sample prior to beginning analyses. Cronbach’s α was 0.81 for the set of seven items on the Interests Scale measuring functional impairment of the child’s primary interest. Individual item internal consistency was strong and ranged from 0.74 to 0.82.

Quantity of interests

ANOVAs controlling for chronological age were run to determine group differences in the total number of current child interests reported by parents. As seen in Table II, the mean number of child interests was similar across groups, with females having slightly more current interests than males. There were no significant differences between children by diagnosis (ASD vs TD; F(1, 86)=0.04, p⩽0.85, η2=0.00) and no significant diagnosis×sex interaction effects (F(1, 86)=0.44, p⩽0.51, η2=0.00).

Content of interests

Mean number of interests by category are reported in Table II. Covarying for chronological age, there were no significant group differences between children’s folk physics interests by diagnosis (F(1, 86)=1.31, p⩽0.26, η2=0.02) or diagnosis×sex (F(1, 86)=0.18, p⩽0.67, η2=0.00). ANOVAs revealed significant differences between groups for folk psychology by diagnosis with children with ASD having fewer folk psychology interests than TD children (F(1, 86)=10.14, p⩽0.01, η2=0.10). Diagnosis×sex effects were also significant, with TD females having the greatest number of folk psychology interests compared to the other groups (F(1, 86)=5.20, p⩽0.03, η2=0.05), followed by TD males and ASD males ASD females who had the fewest current interests in folk psychology and were more similar to ASD males and TD males than their TD female peers (Table II).

A similar percentage of children showed interest in playing solitary games across groups (Table II). However, for social games, group differences were found by diagnosis with significantly fewer children with ASD showing interest in playing games with others than TD children (χ2(1, 87)=15.22, p⩽0.01). Nearly 100 percent of the TD children in this sample were reportedly interested in playing games with others. Diagnosis×sex effects were not significant.

Primary interests

Examples of primary interests across groups are reported in Table III. The primary interests of females and males with ASD were compared (see Figure 1). Though not a significant finding in the primary analysis of the Interests Scale, descriptively, parents reported that males with ASD were much more likely to have a primary interest in physics (e.g. machines, vehicles, spinning objects, physical systems, computers, astrology, sciences, building, Lego®) than all other study groups. A primary interest in physics was most common in males with ASD (n=8), followed by TD males (n=5), ASD females (n=3) and TD females (n=1). The primary interest of females with ASD most commonly fell into the category of TV (e.g. movies, listening to music, YouTube videos, particular shows, tablet watching) or psychology (e.g. relationships, emotions, imagination, pretend figures, live action role play). Notably no males reported an interest in psychology. Though both males and females had primary interests in games, males with ASD were more than twice as likely as females with ASD to have this interest.

Functional impairment of primary interest

Controlling for chronological age, for all seven impairment ratings, parents rated interests in children with ASD as more intense compared to the TD group (Figure 2 and Table II). No sex or diagnosis×sex differences were found for any of these ratings.

Discussion

Our results replicate many of the findings of Turner-Brown et al. (2011). There were no diagnostic differences in the quantity of current interests reported by parents in this sample, but there were significant diagnostic differences in the content and functional impairment of reported current interests. Like Turner-Brown et al., children with ASD in this sample demonstrated significantly more nonsocial/solitary play with their primary interests and their primary interests caused greater functional impairment than peers with TD. It is notable that these findings were replicable in a sample that was balanced by biological sex (51 percent female as compared to 5 percent female), indicating that some aspects of the content and functional impairment of CI are characteristic of the autism phenotype regardless of sex. Even if the interests themselves may be different across sexes, the impact on daily life for children and their families is the same.

In this study, children diagnosed with ASD had significantly fewer folk psychology interests compared to TD children. This parallels a finding that approached significance in the Turner-Brown study, but their significant finding was that children with ASD had significantly greater folk physics interests than TD children. The difference in these results is likely to have been influenced by the larger female representation in both groups in our study sample. TD females were most likely to have interests in folk psychology while females with ASD had the fewest interests reported in this category; the Turner-Brown study had minimal female participants and was underpowered to detect this difference. It also seems that the presence of more females in our sample washed out the effect of folk physics found in the Turner-Brown study. Though children with ASD were more interested in folk physics than TD children, these differences were minimal and not statistically significant in our sample.

Regarding sex differences, there was a significant diagnosis by sex effect for the number of current folk psychology interests. Females with ASD demonstrated the fewest interests in this category and their interests were more closely aligned to males with ASD than to TD males or TD females. This finding is in opposition to recent studies that have indicated that females with ASD have interests more similar to TD females than males with ASD and can therefore “socially camouflage” more effectively than males with ASD (Harrop et al., 2018a; Hiller et al., 2014; Sutherland et al., 2017). Our result offers some support for the “extreme male brain theory” of ASD, which posits that individuals with ASD have average to above average systematizing interests and below average empathy, an extreme version of the typical male brain (Baron-Cohen, 2002, 2010); however, support for this theory is tempered by our lack of significant diagnostic group differences for folk physics interests and the descriptive sex differences in primary interests provided by parents of males and females with ASD.

When children’s primary interests were categorized, males with ASD were much more likely to have a primary interest in the physics category than females with ASD (11 percent of females vs 30 percent of males) and no males with ASD in this sample had a primary interest in the category of psychology compared to 22 percent of females with ASD. Though these results are only descriptive, their contradiction with the quantity of interests in each of these categories illustrates the complexity of both characterizing CI and detecting sex differences in ASD. Our findings indicate that though females with ASD demonstrate a similarly limited number of folk psychology interests to males with ASD, their primary interest is more likely to fall into the category of folk psychology and, therefore, be more aligned with female TD peers. It seems that the interests of females with ASD fall somewhere on a continuum between those of males with ASD and TD females; their interests are not as traditionally female as TD females, but not as traditionally male as males with ASD.

Since the Interests Scale was developed with a male-biased sample, we considered the utility of the Interests Scale for females with ASD. The internal consistency for this sample was nearly identical to the Turner-Brown et al. (2011) study, despite being 51 percent female as compared to 5 percent in the Turner-Brown et al. (2011) sample. This is a strong indication that the functional impairment questions are reliable across sexes in ASD. The Interests Scale categories do seem to probe around the types of interests reported by parents of females; however, the quantity and content of the interests of females may appear typical until parent responses to the functional impairment questions are examined. In our sample, examining parent responses to the functional impairment questions and the social/nonsocial interest question on the Interests Scale would provide the most useful diagnostic information to clinicians.

These findings may have broader implications for diagnostic assessment of school-aged females with ASD. Regardless of how typical the child’s interest seems during behavioral assessment, asking parents about the amount of inclusion of peers vs solitary play around that interest and the degree of functional impairment associated with the child’s interest may be key to identifying ASD. It is also important for clinicians diagnosing ASD to regularly spend time with TD females who, in our sample, demonstrated significantly greater interests in traditionally female or “folk psychology” subjects than all other study groups. This may allow clinicians, who likely spend more time assessing males than females due to the sex imbalance in ASD, to calibrate their expectations of TD females vs ASD and be in a better position to detect mild symptoms or “social camouflaging” in females. It is also possible due to the overlap with TD female peers that the interests displayed by females with ASD may lend themselves more readily to intervention approaches (such as peer modeling and social groups) than interests held by ASD males.

Limitations

Despite a similar ASD sample size to the Turner-Brown study, our TD sample was not matched on size or chronological age. Additionally, as all ASD children were recruited via the (University of North Carolina) ASD Research Registry which requires a clinical diagnosis of ASD for inclusion, we did not repeat gold standard diagnostic tools. Instead we included the SCQ to discriminate between the ASD and TD groups. While this measure did produce a strong group difference, its validity may be weaker for older children (Corsello et al., 2007). Furthermore, the females with ASD who participated in this study were diagnosed using current diagnostic practices, and therefore, our sample may be biased toward females who present like ASD males. Future research would benefit from recruiting “sub-threshold” females, who do not quite meet criteria for an ASD diagnosis, or recruiting larger samples of females across the functioning spectrum to understand how our findings associate with functioning/severity.

Conclusions

Overall our findings strengthen the results of Turner-Brown et al. (2011), with more nonsocial interests and greater functional impairment associated with interests in children with a diagnosis of ASD compared to TD controls. However, descriptively males and females with ASD differed in the content of their primary interest, with ASD female interests aligning more with those reported in typical development. Our findings have implications for how CI are assessed within clinical practice and the importance of considering gender when working with females with ASD.

Figures

Percent of females vs males with ASD with primary interests in each category

Figure 1

Percent of females vs males with ASD with primary interests in each category

Mean functional impairment ratings from the interests scale by study group

Figure 2

Mean functional impairment ratings from the interests scale by study group

Sample characteristics

Females Males
ASD (n=27) TD (n=17) ASD (n=27) TD (n=16) Diagnosis effects
Chronological age (months) 101.33 (17.46) 94.71 (17.46) 113.48 (10.10) 83.99 (17.85) F(3, 86)=7.68, p⩽0.01*
Mental age from DAS-2* (months) 102.51 (29.78) 114.17 (24.00) 118.03 (27.01) 127.32 (40.43) F(3, 79)=2.23, p⩽0.09
SCQ* total score 13.92 (5.02) 2.05 (2.83) 14.92 (5.94) 3.5 (2.58) F(3, 82)=42.83, p⩽0.01*
RBS-R* total score 35.88 (22.85) 5 (8.63) 29.70 (16.57) 3.13 (2.87) F(3, 85)=21.88, p⩽0.01*

Notes: DAS-2, Differential Ability Scales (Elliot, 2007); SCQ, Social Communication Questionnaire (Rutter, Bailey and Lord, 2003); RBS-R, Repetitive Behavior Scales – Revised (Bodfish et al., 1999). Mean (SD) unless otherwise noted. *Statistically significant at the 0.05 α level

Interests scale mean (SD) scores for all study groups and group comparison effects controlling for chronological age

Girls Boys
ASD (n=27) TD (n=17) ASD (n=27) TD (n=16) Diagnosis effect (F ratio, p-value, η2) Diagnosis×Sex effect (F ratio, p-value, η2)
Number and content
Number of current interests 14.33 (6.58) 15.24 (7.35) 12.41 (5.77) 11.88 (6.15) F(1, 86)=0.04, p⩽0.85, η2=0.00 F(1, 86)=0.44, p⩽0.51, η2=0.00
Number of folk psychology interests 1.11 (1.01) 2.41 (1.00) 1.19 (1.08) 1.44 (0.89) F(1, 86)=10.14, p⩽0.01*, η2=0.10 F(1, 86)=5.20, p⩽0.03*, η2=0.05
Number of folk physics interests 2.19 (1.66) 1.94 (2.01) 2.56 (1.89) 2.13 (1.75) F(1, 86)=1.31, p⩽0.26, η2=0.02 F(1, 86)=0.18, p⩽0.67, η2=0.00
% interested in social games 63 94.12 62.97 100 χ2(1, 87)=15.22, p⩽0.01* χ2(1, 87)=1.27, p⩽0.26
% interested in playing alone 77.78 58.82 77.78 68.75 χ2(1, 87)=2.59, p⩽0.11 χ2(1, 87)=0.07, p⩽0.79
Impairment ratings
Overall degree of interest (1–3) 2.81 (0.48) 2.47 (0.51) 2.89 (0.32) 2.75 (0.45) F(1, 86)=5.16, p⩽0.03*, η2=0.06 F(1, 86)=1.07, p⩽0.30, η2=0.01
Frequency of activity (0–3) 3.78 (0.85) 3.18 (0.88) 3.56 (0.89) 3 (0.63) F(1, 86)=9.76, p⩽0.01*, η2=0.10 F(1, 86)=0.00, p⩽0.99, η2=0.00
Degree of interference (0–3) 1.67 (0.96) 0.59 (0.87) 1.41 (0.80) 0.56 (0.63) F(1, 86)=21.73, p⩽0.01*, η2=0.20 F(1, 86)=0.43, p⩽0.51, η2=0.00
Degree of resistance (0–3) 1.67 (0.92) 0.82 (0.64) 1.74 (0.71) 1 (0.82) F(1, 86)=13.92, p⩽0.01*, η2=0.13 F(1, 86)=0.28, p⩽0.60, η2=0.00
Degree of flexibility (0–3) 1.48 (0.80) 0.59 (0.62) 1.41 (0.84) 0.94 (0.68) F(1, 86)=16.10, p⩽0.01*, η2=0.17 F(1, 86)=1.03, p⩽0.31, η2=0.01
Accommodation required (0–3) 1.37 (0.97) 0.29 (0.47) 1.37 (0.97) 0.31 (0.60) F(1, 86)=26.30, p⩽0.01*, η2=0.23 F(1, 86)=0.02, p⩽0.88, η2=0.00
Involvement of people (0–3) 1.96 (0.60) 1.24 (0.83) 1.89 (0.80) 1.40 (0.81) F(1, 86)=7.87, p⩽0.01*, η2=0.08 F(1, 86)=0.92, p⩽0.34 η2=0.01
Total intensity rating 13.08 (2.78) 8.35 (2.99) 12.52 (2.89) 8.94 (1.91) F(1, 86)=38.49, p⩽0.01*, η2=0.30 F(1, 86)=0.91, p⩽0.35, η2=0.01

Notes: Mean (SD) unless otherwise specified. *Statistically significant at the 0.05 α level

Examples of children’s primary interests by group and category

ASD TD
Primary interest category Boy examples Girl examples Boy examples Girl examples
TV Playing on tablet Watching and making videos on YouTube, tablet, Paw Patrol®, listening to music Watching TV, tablet, Paw Patrol®, audio books
Taxonomy Pokémon® cards
Sports Basketball, sports Soccer Gymnastics, dance
Sensory Drumming, percussion
Psychology Playing with dolls, My Little Pony®, LOL Surprise® dolls, Littlest Pet Shop® figures, Barbie® Dolls, Character/Dramatic Play Fashion, stuffed animals
Physics Trains, Lego®, cars, computers, electronics John Deere® tractor, electronics Lego®, computer science, cars, trucks Lego®
People Harry Potter
Math Watches, math video games Mathematical calculations
Language Reading Reading
Games Video games, Minecraft®, iPad games Video games, Bop-it® Game, Mario Brothers® Video games, Terraria®, Minecraft®, Online or board games, Playing games with others Playing games with others, Minecraft®
Facts World War I
Crafts Computer animation Drawing, painting, coloring, drawing characters and cutting them out Drawing, sculpture, writing a book Creative writing
Biology Dinosaurs, animals Dinosaurs Animals

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Corresponding author

Sallie Wallace Nowell can be contacted at: sallie7@ad.unc.edu

About the authors

Sallie Wallace Nowell is based at the Frank Porter Graham Child Development Institute, The University of North Carolina at Chapel Hill, Carrboro, North Carolina, USA.

Desiree R. Jones is based at the School of Behavioral and Brain Sciences, The University of Texas at Dallas, Richardson, Texas, USA.

Clare Harrop is based at the Department of Allied Health Sciences, The University of North Carolina at Chapel Hill, Carrboro, North Carolina, USA.