Introduction
The broad autism phenotype (BAP) has been described as a set of subthreshold features qualitatively similar to those existing in autism spectrum disorder (ASD), which is continuously distributed and spreads beyond ASD family members into the general population (Constantino & Todd,
2003; Hoekstra et al.,
2007; Hurst et al.,
2007; Stewart & Austin,
2009). As pointed out by numerous authors (e.g., Morrison et al.,
2018; Wainer et al.,
2011), BAP traits correspond directly to the primary characteristics of ASD: Social Communication and Social Relation Impairment (SCI) alongside a Pattern of Restricted Repetitive Behaviours and Interests (RRBs; American Psychiatric Association [APA],
2013). Even though the definition of ASD has been updated over time, the most popular BAP definition has barely changed and has not been revised according to the most recently updated definition of ASD (APA,
2013). This has generated a discrepancy between ASD and BAP conceptualizations that, in our opinion, needs to be addressed.
The reharmonization of the BAP and ASD constructs will highly contribute to the field as it will operationalize the BAP in the spectrum, increasing its understanding and, providing further information regarding how core autistic deficits are expressed differentially on each severity level. Likewise, it will also help to uncover autistic genetic mechanisms (Gaugler et al., 2014; Robinson et al., 2011) by exploring the presence of BAP in parents of children diagnosed with ASD. In the same way, it will also increase the understanding of the developmental path of autism in elder adults (Stewart et al., 2018) which has not been very studied yet. Finally, we can as well take advantage of BAP samples to test assessment and intervention procedures before applying them to clinical and more sensible samples.
On the other hand, accepting that both constructs essentially represent the same spectrum of traits to a different degree, could bring many advantages for several populations. As such, uncertain cases of those individuals who do not have a clear ASD diagnosis but have shown highly impaired BAP behaviors and, in lower intensity, independent and functional adults with some core autistic behaviors that impoverish their social interactions, as well as those capable of camouflaging or smoothing specific deficits (developing ways to cope with them; Hull et al., 2017; Livingston et al., 2019; Mandy, 2019), could also benefit from well-established autism assessment protocols and interventions which will represent, indeed, a clinical milestone.
In this regard, the reconciliation of BAP and ASD will drive certainly to restore any previous measurement process. According to the Standards (2014), whether two tests have defined the same construct differently and, thus, contain different internal structures, those tests are assessing essentially two different things. The BAP, as the autistic phenotype, has been proposed to share ASD internal structure, and, consequently, tests that aim to measure the BAP should be developed upon an updated two-factor internal structure. Conducting studies to establish conclusions on ASD populations through BAP samples necessarily imply the existence of a measurement tool capable of measuring an updated BAP operationalization. For all the abovementioned reasons, in this work, we aimed to confirm whether it is possible to integrate the items of the most frequently used tests for assessing the BAP to provide a BAP measure that would be aligned with the current operationalization of ASD.
The Outdated Operational Definition of the BAP
The BAP was first reported by Leo Kanner (
1943) who observed that the parents of children diagnosed with ASD presented subtle expressions of autistic-like traits such as an obsession with details, social awkwardness, and rigid behaviours. Later, more formal investigations conducted by Piven et al., (
1997a,
1997b) identified autistic-like core deficits in first-degree relatives of people diagnosed with ASD. Those deficits established the foundations for the first operational definition of BAP, which was developed by Hurley et al. (
2007), who, after reviewing outcomes of the studies conducted in the previous two decades, defined the BAP as a set of subclinical personality characteristics and language deficits clustered around three main domains; aloof personality, rigid personality, and pragmatic language impairment paralleling its definition with that proposed for ASD by the DSM-IV-TR (American Psychiatric Association [APA],
2000).
According to the literature, an aloof personality involved a lack of social responsiveness (Constantino et al.,
2006), reduced social abilities (Wheelwright et al.,
2010), and scarce social engagement (Whitehouse et al.,
2010). Likewise, a rigid personality was manifest in behavioural rigidity, a tendency toward perfectionism, stubbornness, and stereotyped behaviours (e.g., Losh et al.,
2008; Murphy et al.,
2000; Narayan et al.,
1990). Finally, pragmatic language deficits were related to supra-linguistic aspects such as problems in respecting turn-taking in speaking, becoming side-tracked in conversations, and difficulties in maintaining the topic of conversations (Seidman et al.,
2012).
Although this is now a more mature field, there is still no universal agreed operationalization of the BAP, but rather a quantitative and qualitative amalgam of traits that vary according to the measurement method used to assess the phenotype (Wainer et al.,
2011). Those varied features have been, sometimes, difficult to cluster so as to conform to a consensual structure for the BAP enabling to reinsert it inside the autism continuum. In light of more recent research, it makes no sense that the phenotypic expression of ASD, which had emerged for improving the knowledge about its aetiology, would diverge from its mother disorder and, thus, consensus could be reached in the conceptualization of the BAP by aligning it with the updated definition of the ASD (APA,
2013). According to this definition, ASD has been defined as a continuum of increasing severity. Some authors have previously argued in favour of this idea, associating the lesser, non-clinical expressions of autism, with the BAP (Bolton et al.,
1994; Constantino & Todd,
2003; Piven & Palmer,
1999). In this regard, some studies have already proposed that the BAP should comprise only two characteristic traits, these being conceptualized as both social and non-social expressions of the BAP, where social traits have included both social impairment in social relations and in social communication; whilst non-social traits have constituted a rigid personality (Morrison et al.,
2018; Sasson et al.,
2013b).
The Measurement of the BAP
Although the BAP has traditionally been assessed through structured and extensive interviews designed to evaluate personality (i.e., M-PAS-R; Piven et al.,
1994), the use of brief psychometric self or informant-reports has increased, reducing time costs and enhancing objectivity. Among these questionnaires, the Autism Spectrum Quotient (AQ; Baron-Cohen et al.,
2001), the Social Responsiveness Scale (SRS; Constantino & Gruber,
2005), and the Broad Autism Phenotype Questionnaire (BAPQ; Hurley et al.,
2007) have been the most widely used (for a review see, Ingersoll & Wainer,
2014).
Despite having plenty of benefits, researchers and clinicians should be particularly careful regarding the theoretical and empirical evidence supporting the interpretation of these test scores. In particular, following the changes in the operationalization of ASD from three to two general domains (APA,
2013), it might be advisable to draw special attention to different sources of validity evidence such as the internal structure or test content. Adverse evidence would imply the need to question the interpretation of the test scores (American Educational Research Association, American Psychological Association, & National Council on Measurement in Education [AERA, APA, & NCME],
2014). As stated above, there has been a lack of correspondence between the operationalization of the BAP (understood as the subclinical expression of autism which includes both impairment in social interactions and rigid behaviours) and the content of the tests most frequently used for its evaluation. Of equal importance is the fact that this lack of correspondence could also be observed between the operationalization of the construct and the internal structure of these tests.
The three aforementioned measures have reflected this lack of correspondence. Thus, the AQ—which was originally designed for assessing autism in adults with typical-range IQs—comprises five content-domains and five factors: Social Skills, Attention Switching, Attention to Detail, Communication, and Imagination (Baron-Cohen et al.,
2001). In spite of contradictory data in the literature, some studies have supported the clustering of the five subscales into a three-factor model: Social skills, Details/patterns, and Communication/mindreading (English et al.,
2019; Hurst et al.,
2007; Russell‐Smith et al.,
2011). Similarly, the second adult version of the SRS (SRS-2) measures autism in adults with typical development and includes five subscales: Social Awareness, Social Cognition, Social Communication, Social Motivation, and Restrictive and Repetitive Behaviors (Bruni,
2014; Constantino & Gruber,
2012). It includes two subscales compatible with the DSM-5: Social Communication and Interaction, and Restricted Interests and Repetitive Behaviours. Scores on these subscales have facilitated the comparison of symptoms with DSM-5 diagnostic criteria for ASD. These comparisons could help to determine whether a person meets the most current diagnostic criteria for ASD (Constantino & Gruber,
2012). As support for this idea, Frazier et al. (
2014) observed that SRS-2 subscales could be encompassed by the following two-structured factors: Social Communication/Interaction (SCI), and Restricted/Repetitive Behavior (RRB; Frazier et al.,
2014). Finally, the BAPQ, the tool originally designed for assessing the BAP in parents of children diagnosed with ASD, includes three factors: Aloofness, Pragmatic Language Deficits, and Rigidity (for a review, see Hurley et al.,
2007; Sasson et al.,
2013a).
Despite the diverse specifications of these tests, some authors have suggested that these all could serve to assess the same underlying BAP structure. In an attempt to search for the similarities between these tests and to obtain an empirically-based latent structure of the BAP in a non-clinical sample, Wainer et al. (
2011) conducted a conjoint exploratory factor analysis by collapsing the AQ, the SRS-A (adult self-report version; Constantino & Gruber,
2005), and the BAPQ subscales. They concluded that the subscales could conform to a three-factor structure similar to that proposed for ASD by the DSM-IV-TR (APA,
2000). These three factors, named Aloof Personality, Pragmatic Language Difficulties, and Rigid Personality, matched with the BAPQ factors and with one of the most accepted descriptions and operationalizations of the BAP (Piven et al.,
1997a,
1997b).
In view of their findings, Wainer et al. (
2011) also discussed their resulting BAP structure and suggested that more research was needed to clarify whether the core areas of impairment observed in ASD (and, by extension, the BAP as its non-clinical expression) could be grouped into two core domains. This was in line with recent literature that has suggested the need for a new conceptualization of the phenotype aligned with the current definition of ASD (APA,
2013), centred around two core domains: social and non-social areas (Morrison et al.,
2018; Sasson et al.,
2013b).
To take the work of Wainer et al. (
2011) one step further, the present study aimed to extend and revise their findings by exploring the connection between the AQ, the BAPQ, and the SRS-2 subscales with an updated conceptualization of BAP according to two main dimensions or domains: Deficits in Social Communication and Social Interaction (hereafter, SCI BAP) and Restricted, Repetitive Patterns of Behaviours, Interests, or Activities (hereafter, RRB BAP). To this end, our study firstly explored the internal structure resulting from applying parallel analysis (Horn, 1965) to the set of total scores of each subscale of the mentioned tests (first objective, parallel analysis). Secondly, we took the first step towards bridging the gap between the operationalization and measurement of the BAP by selecting the most relevant items for its measurement. For this second objective, a group of collaborators from our research lab allocated the items of these questionnaires, according to their content, to the seven ASD subdomains (Loevinger,
1957). Furthermore, they verified their itemmetric properties (see Angleitner et al.,
1986; Grant & Davis,
1997).
Finally, we recollected quantitative information regarding content validity (Lynn,
1986). For achieving our third objective, a broad group of experts evaluated the relevance (Ebel & Frisbie,
1972; Haynes et al.,
1995) and the representativeness (Haynes et al.,
1995; Lynn,
1986) of the selected items for assessing BAP features based on the updated operationalization aligned with the current definition of ASD (Armstrong et al.,
2005; Beck & Gable,
2001; Delgado-Rico et al.,
2012).
Following the results presented in Wainer et al. (
2011), we hypothesized, that the subscales of the AQ, the BAPQ, and the SRS-2 could be clustered into three components of variance that could correspond to the original conceptualization of BAP (first objective; Hurley et al.,
2007; Piven, et al.,
1997a,
1997b). Further, we expected to find some problems regarding the formal aspects of items (second objective; see Angleitner et al.,
1986). For instance, some items could present high levels of social desirability, low levels of self-reference, lack of concreteness or be difficult to understand. In addition, since items stem from different tests with different operationalizations of the BAP (in the case of BAPQ) and ASD (in the case of AQ and SRS-2), we hypothesized that their relevance for assessing one of the seven BAP subdomains could equally affect their final selection (third objective). For example, Item 11 SRS-2 states “I have got self-confidence” which could not be relevant since it did not capture any of the key contents of the seven BAP subdomains. Finally, since the items were constructed within the framework of previous BAP or ASD definitions, we anticipated that some of the seven BAP subdomains could be under-represented (third objective).
Discussion
The purpose of this study was to connect the content of three current BAP measurement tools with an updated operationalization of the BAP harmonized with the ASD one (APA,
2013). The underlying idea was to detect possible gaps in the contents of BAP measurement instruments and to take a preliminary step towards bridging the gap between the operationalization and measurement of this phenotype.
First, we conducted a parallel analysis (Horn, 1965) to assess the factor structure of the BAP across the AQ, the BAPQ, and the SRS-2 subscales (Hurley et al.,
2007; Piven, et al.,
1997a,
1997b). Unlike the findings reported by Wainer et al. (
2011), our results pointed to two main components instead of three. The fact that the three most applied BAP tests can cluster the variance of their 13 scales into two components provides an empirical basis for updating the BAP operationalization to a construct that uses two principal domains aligned with the current definition of ASD (APA,
2013). These results are consistent with those presented previously providing empirical evidence for the correspondence between BAP and ASD dimensions. For example, Sasson and et al., (
2013c) observed that socio-communicative aspects of the BAP (measured by the Aloof and Pragmatic Language subscales of the BAPQ), unlike non-social features (measured by the BAPQ Rigid subscale) were connected to social skill and social cognition whilst also predicting poorer performance in social areas. In another study, Frazier et al. (
2014) examined the SRS-2 factor structure and considered a simpler two-factor solution that showed the correspondence between SRS-2 and current ASD dimensions.
Second, we explored whether the available self-reported tests were adequate for evaluating BAP according to its updated definition. The study of the phenotype requires an adequate measurement tool that cannot disregard the actual structure and specifications of the construct. Thus, both, theoretically and empirically-based claims regarding the two-dimensional structure of the BAP (e.g., Morrison et al.,
2018; Sasson, et al.,
2013c) formed the basis of the main goal of this study: to reallocate its items (i.e. relevant BAP behaviours or preferences) according to the two main subdomains of ASD in the DSM-V (APA,
2013).
With respect to this allocation phase, two main observations are worth noting. All the BAPQ items were distributed across different subdomains of the proposed BAP operationalization but they did not sufficiently cover all the subdomains. That is, whilst BAPQ items might accurately evaluate subclinical autistic-like traits according to the DSM-5, the inferences based only on its items would be limited and not representative of the actual BAP construct. The SRS-2, however, with its higher number of items and contents, taps into all BAP subdomains and gathers more types of BAP-related behaviours and preferences than the BAPQ and the AQ. However, at the same time, some SRS-2 items were considered to not fit in any subdomain. Consequently, applying only the SRS-2 when measuring autism traits could cover all autistic-like features, together with some other non-autistic related deficits, which could blur the interpretation of its scores. On balance, we conclude that, when used alone, all of the proposed tests are insufficient for assessing the updated BAP operationalization. Consequently, the next step was to test whether a conjoint use of the items of the three tests would more adequately represent the BAP construct.
Third, before studying the relevance and representativeness of all these items for measuring BAP (Expert judgment 2), their wordings were scrutinized to ensure that any problem regarding their itemmetric properties would not affect the work of the experts. It is worth highlighting the importance of eliminating poorly drafted items that could yield biased responses, since these could affect the way respondents interpret and answer them (see Angleitner et al.,
1986; Grant & Davis,
1997), along with the way the construct is finally assessed (Haynes et al.,
1995). Furthermore, some populations, particularly BAP people, have problems when they are required to put themselves in the position of others. Consequently, they may struggle to answer items regarding others’ view of the person (non-self-referred items). As we hypothesized, some formal problems emerged during the itemmetric judgment, and half of the items were discarded in this analysis. The item property that appeared to be the most problematic was concreteness. The experts suggested that some items were too generic and/or refer to more than one idea (e.g., SRS-2 item 30 refers to more than one idea) whilst others were unclear (e.g., AQ Item 15 uses an adverb that interferes with the rating scale) or did not involve self-reference.
Fourth, we examined the relevance and representativeness of the items for covering the whole BAP construct (Haynes et al.,
1995; Lynn,
1986; Nunnally & Bernstein,
1994; Suen & Ary,
1989). By doing this, the initial set of items was reduced by less than a third. In addition, both expert judgments indicated an unbalance in the distribution of items throughout the domains and subdomains where the number of items in SCI BAP was more than twice those in RRB BAP. This unbalance could be due to discrepancies in the original operationalizations of the targeted construct of each test. The BAPQ was developed based on a three-dimensional BAP structure (Hurley et al.,
2007), while the AQ also included aspects of cognitive abnormality (Baron-Cohen et al.,
2001). Similarly, the SRS originally aimed to assess autistic social impairment, particularly reciprocal social behaviours (Constantino & Todd, 2005) although the most recent version of this questionnaire, the SRS-2, includes a new subscale for the assessment of restricted and repetitive behaviours (Constantino & Gruber,
2012).
This asymmetric representation of domains could be challenging, given that many authors have claimed that both are important for diagnosing autism since the time that Kanner (
1943) provided the first accurate definition of the disorder. Accordingly, and as now detailed in the DSM-5, the three SCI subdomains and at least two RRB subdomains must hinder the person’s everyday life to be regarded as a conclusive ASD diagnostic (APA,
2013). The same can be applied to BAP assessment such as the non-clinical expressions within the autism spectrum. Furthermore, the experts (Expert judgment 2) in our study considered that the BAP construct was well represented by the two domains and seven subdomains included in the definition we provided based on the autism spectrum definition (DSM-5; APA,
2013). These results support our claim for the need to evaluate both SCI and RRB domains equally when studying BAP.
The experts also pointed out that the selected items were representative of the construct. Although the content of the items could appear to be sufficiently representative of the BAP construct, the final allocation presents clear gaps in the BAP content. Thus, we should not disregard the underrepresentation of two RRB subdomains and its theoretical and psychometric implications. Since autism shares some indicators with other disorders, the worst scenario that could arising from neglecting certain key autistic behaviours (e.g., Hyper/hypo-reactivity to sensory input or unusual interest in sensory aspects) in preliminary test construction phases could lead to variations in final test scores that only reflect differences in traits that are also shared with other disorders.
In this regard, some studies have reported that the RRB domain can be divided into two clusters of indicators: (a) repetitive motor and sensory behaviours (repetitive hand movements) and (b) insistence on sameness (narrow interests, rigid routines, and rituals; Cuccaro et al.,
2003; Honey et al.,
2012; Richler et al.,
2007). Assessing only one of the two RRB subtypes could lead to ASD variations being confounded with other disorders such as social communication disorder (characterised by persistent deficits in the social use of verbal and non-verbal communication in the absence of restricted and repetitive interests and behaviours; APA,
2013) or obsessive–compulsive disorder (the assessed person could not meet the criteria for the second subdomain). This would have a direct effect on BAP identification and future research studies, particularly those concerned with neurobiological and genomic aspects (Ruscio & Ruscio,
2002,
2004). For instance, there is evidence that the subdomains of RRB are underpinned by different neural pathways (Langen et al.,
2011). Thus, a lack of relevant items with which to assess stereotyped or repetitive motor movements, use of objects, or speech, could negatively affect the study of the different neural pathways of autism, either in people diagnosed with autism or BAP family members.
In conclusion, researchers have begun to highlight the need to update the definition of BAP so that it is aligned with the current definition of ASD (Morrison et al.,
2018; Sasson, et al.,
2013c). This study represents a first step towards achieving this goal by providing empirical evidence in support of the need for a new test for evaluating the BAP that runs parallel to the ASD structure, containing its most relevant content but also including additional indicators that measure milder forms of ASD.
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