Multidimensional Scaling of the Wechsler Intelligence Scales for Children in a Clinical Sample Assessed for Fetal Alcohol Spectrum Disorder (FASD)

Alcohol is a potent teratogen that readily crosses the placenta to disrupt prenatal development (Mattson et al., 2019). Fetal Alcohol Spectrum Disorder (FASD) is a diagnostic term used to encapsulate the various behavioural, physiological, and neurodevelopmental challenges arising from prenatal alcohol exposure (Shelton et al., 2018). FASD is a significant public health concern and a leading cause of developmental disability within the western world (Astley, 2004), affecting approximately 7.7 per 1000 children in the general population (Lange et al., 2017). Although children with prenatal alcohol exposure may present with a range of physical, neurological, and psychological abnormalities, cognitive deficits are the most consistent feature of FASD, with impairment most frequently observed in working memory, attentional processes, executive functions, visuospatial reasoning, language, and general intelligence (Coriale et al., 2013; Shelton et al., 2018). Despite this, the occurrence and severity of cognitive impairment varies significantly between cases, providing an obstacle to the clinical assessment of FASD (Benz et al., 2009).

FASD is underrecognised globally, with inconsistent assessment approaches and limited access to diagnostic services providing barriers to disease identification (Hayes et al., 2023). As a consequence, many children with prenatal alcohol exposure may be at risk of receiving insufficient support for the neurodevelopmental challenges associated with FASD. Establishing sophisticated diagnostic considerations for the clinical assessment of FASD is therefore imperative to better equip clinicians with the skillset to disentangle the complex phenotypes associated with prenatal alcohol exposure. International guidelines currently inform clinical practice (Astley, 2004; Bower et al., 2016; Cook et al., 2016), though they are not without criticism (Hayes et al., 2022; McLennan & Braunberger, 2017). For instance, stakeholders have identified a disconnect between conceptualisations of cognitive functions described by international diagnostic guidelines and neuropsychological theory underpinning the assessment tools recommended to assess latent cognitive constructs in children with prenatal alcohol exposure (Hayes et al., 2022; McLennan & Braunberger, 2017). The result of this divide is the underutilisation of rich psychometric research that could better inform the assessment of FASD-related cognitive deficits. Bridging the gap between psychometric theory and the current clinical guidelines is critical to improving the consistency and accuracy of FASD diagnosis. Such changes may reduce reliance on clinical intuition, allowing for a standardised and systematic approach to patient-centred care.

The Cattel-Horn-Carrol (CHC) theory of human cognition is a psychometric taxonomy that emphasises the covariance between aspects of intelligence and cognitive functionality (Caemmerer et al., 2020). The CHC model is organised hierarchically, with stratum III representing the general factor of intelligence or ‘g’, stratum II representing 16 broad cognitive abilities, and stratum I representing over 80 narrow abilities (Jewsbury et al., 2017; McGill & Dombrowski, 2019). The CHC model is largely congruent with many existing intelligence tests (Flanagan & Alfonso, 2017; Flanagan et al., 2013), including the Wechsler Intelligence Scales for Children (WISC), commonly recommended as a cognitive assessment tool for FASD diagnostic purposes (Bower et al., 2016; Cook et al., 2016).

While the fourth edition of the WISC (WISC-IV) is typically interpreted through four primary indices (Wechsler, 2003), CHC-derived models propose a five-factor structure, with the primary subtests purported to measure fluid reasoning (Gf), visuospatial processing (Gv), crystalised intelligence (Gc), short-term memory (Gsm), and processing speed (Gs) (Flanagan et al., 2013; Keith et al., 2006). Despite deviating from the standard WISC-IV interpretation, the invariance of the CHC-derived five-factor structure is supported cross-contextually (Chen et al., 2009; Golay et al., 2013; McGill & Canivez, 2018) and is suggested to retain validity irrespective of neurodevelopmental and intellectual disability (Weiss et al., 2013). Meanwhile, the fifth edition of the WISC (WISC-V), organises the test into five primary indices representing visual processing (Gv), fluid reasoning (Gf), crystalised intelligence (Gc), short-term memory (Gsm), and processing speed (Gs) CHC abilities (Chen et al., 2015; Wechsler, 2014). The invariance of this structure in neurodevelopmentally disordered populations is supported by the WISC-V administration manual, which details the test’s utility in a normative sample that includes a proportion of children with various special education classifications (i.e. Intellectual Disability, Specific Learning Disorder, Autism Spectrum Disorder, Attention-Deficit/ Hyperactivity Disorder and children considered intellectually gifted: Wechsler, 2014). Table 1 outlines the proposed congruency between the CHC model and WISC primary indices/subtests.

Since both WISC-IV and WISC-V CHC-derived models assert construct validity among neurodevelopmentally disordered populations, the purported structure of these tests should be retained when examining children with prenatal alcohol exposure, where diverse and complex impairments across cognitive functions are common. To assess this, a robust investigation into the CHC-derived factor structure of the WISC-IV and WISC-V models within children with prenatal alcohol exposure is warranted. Such research will help to better understand whether the current diagnostic paradigm with a CHC theoretical framework is valid, reliable, and useful to clinical practice.

The present study utilised archival data collected by a tertiary FASD clinic located in Queensland, Australia, between 2014 and 2018. Data were extracted from a de-identified research database containing information recorded in medical records, parallel files, and computer scoring programs as part of the standard clinical care model. The sample included children referred to the clinic due to behavioural problems and/or suspected neurodevelopmental problems, and a background of confirmed prenatal alcohol exposure. Demographic and background information were collected during the detailed clinical intake interview. A standardised assessment of cognition, utilising either the WISC-IV or the WISC-V A&NZ, was administered by a clinical neuropsychologist or clinical psychologist, consistent with recommendations in the Australian guide to Diagnosis of FASD (Bower et al., 2016). The ten core subtests of the WISC-IV and WISC-V models were administered following the standardised administration procedures and scored using standard scoring procedures.

When required, WISC administration was adjusted in-line with standardised procedures specified in the administration manuals to accommodate attention, language, motor, and other delays. A range of common accommodations were also used when necessary, including regular breaks or compliance-reward activities between subtests (i.e. playing a quick card game). Less common adjustments included the presence of support persons for emotional regulation, adjustable furniture for musculoskeletal difficulties, and adjustments to lighting and ambient sound for sensory issues. The full WISC was administered to all children. However, in accordance with standardised administration and scoring procedures, subtests were awarded a raw score of zero in cases where children engaged with a subtest but could not complete items and no score was recorded when a child could not validly engage with a subtest. Supplementary subtests were administered only when clinically necessary. These data were utilised to inform clinical decision-making, but not included in the current study.

The WISC-IV sample (n = 87) consisted of 56 males (64.4%) and 31 females (35.6%), with ages at the time of assessment ranging from 6.92 to 13.17 years (M = 9.05, SD = 1.64). The WISC-V sample (n = 21) consisted of 16 males (76.2%) and 5 females (23.8%) with ages at the time of assessment ranging from 7.25 to 13.80 years (M = 9.07, SD = 1.66). A missing value analysis identified approximately 5% missing data across all WISC-IV/V subtests, indicating that the dataset was suitable for analysis. PROXSCAL employs listwise exclusion of cases for missing data. Little’s Missing completely at random (MCAR) assessment was utilised to validate any exclusion. MCAR was not significant (p > .05) for both WISC-IV and WISC-V samples, indicating that missing data was completely random. Tables 2 and 3 outline descriptive and demographic statistics for the WISC IV and WISC-V samples.

The present study offers a novel perspective on the standardised assessment of intellectual ability in a cohort of children with prenatal alcohol exposure. While preliminary, due to sample size and methodology, our results indicate that a CHC-oriented interpretation of the WISC-IV and WISC-V may be unsuitable within this clinical context, with the relative positioning of subtests deviating from expectations of test complexity and structure reported in prior literature.

CHC-derived WISC-IV short-term memory (Gsm) and crystalised intelligence (Gc) subtests clustered in close proximity to each other and were positioned towards the centre of the radex, indicating shared content features and greater cognitive complexity of these tasks within the sample. Clustering between CHC-derived visuospatial processing (Gv) and fluid reasoning (Gf) subtests was also observed in the WISC-IV model, suggesting poor discrimination between these domains. Interestingly, the standard four-factor WISC-IV index framework is structured so that Gf and Gv subtests represent a single perceptual reasoning domain. Our findings indicated that the standard interpretation of the WISC-IV perceptual reasoning index may be more suitable for this clinical cohort than a CHC-derived assessment.

WISC-V subtest clustering indicated general associations between fluid reasoning (Gf) and working memory (Gsm) subtests, crystalised intelligence (Gc) and working memory (Gsm) subtests, and fluid reasoning (Gf) and visuospatial reasoning (Gv) subtests, suggesting interdependencies between these domains within the sample. The within-domain dispersion of subtests within this sample also indicated poor relationships between tasks purported to measure the same domain. The exception to this were processing speed (Gs) tasks, which appeared to have a close within-domain relationship and a general dissocation from other tasks administered to the sample.

Working memory tasks appeared more centrally than typically expected across both WISC-IV and WISC-V configurations (Chen et al., 2015; Keith et al., 2006; Weiss et al., 2013). Contextually, this implies elevated task complexity of Gsm subtests within this sample and may represent a deficit in working memory commonly reported for children exposed to alcohol in utero (Coriale et al., 2013). Such findings, however, should be interpreted with caution, as collectively, outcomes suggested that the WISC models may be limited in discriminating between CHC domains within this cohort.

While sample-specific characteristics may underpin the observed discrepancies with prior findings and reflect the variable cognitive profile often observed in children with prenatal alcohol exposure (Akison et al., 2024), considerable debate persists regarding the overall utility of index scores beyond higher-order ‘g’ for understanding intelligence profiles in both normative and clinical populations. Higher-order ‘g’ is often noted as the predominant source of variance within WISC models (Canivez et al., 2017; Canivez & Kush, 2013; Dombrowski et al., 2015; Watkins, 2006, 2010). On this basis, it has been claimed that WISC assessments psychometrically detect overall IQ more accurately than domain-specific cognitive abilities. Dombrowski et al. (2018) describe index-level interpretation of the WISC as heavily dependent on the gradual differentiation of cognitive constructs that occurs as children age (Dombrowski et al., 2018). As neurodevelopmental disorders often limit the maturation and diversification of cognitive functions, it is conceivable that such conditions could impinge upon the efficacy of the WISC in accurately detecting latent cognitive abilities among these populations. However, solely interpretting overall IQ scores, while psychometrically robust, severely diminishes the clinical utility of these tools in determining the extent of domain-specific functional impairment among disordered groups (Courville et al., 2016; Fiorello et al., 2007; Hayes et al., 2022; McGill, 2016). Furthermore, some evidence supports the use of index-level interpretation above overall IQ in clinical groups, emphasising the importance of individualised assessment in neurodevelopmentally delayed children (Fiorello et al., 2007). As such, it is crucial to consider alternative interpretation frameworks that may complement and enhance standard psychometric approaches to facilitate a stronger understanding of functional deficits.

The ‘Boston Process Approach’ is a philosophical ideology within clinical neuropsychology that emphasises the importance of the process taken in responding to intelligence tests, particularly within clinical settings, where the extent of an individual’s functional impairment fundamentally defines the interaction between input and output features of cognitive tasks (Bruno-Golden et al., 2013; White & Rose, 1997). Hence, understanding the patient’s ability (process-success) or inability (process-failure) to complete a task may provide insight into the practical implications of neurocognitive impairment, offering a richer understanding of how cognitive deficits may manifest in everyday functioning (Bruno-Golden et al., 2013). In this context, the administration modality of a task (or what Guttman initially referred to as ‘The Facet of Format of Communication’) becomes particularly important, as the ease or difficulty in which an individual responds to each modality may be informative for understanding functional abilities.

Our results (illustrated in Figures 3 and 4) demonstrated the utility of such an alternative interpretation framework, with WISC-IV and WISC-V MDS outputs illustrating a pattern of subtest clustering that adhered to response modality. Upon interpretation, WISC-IV subtest clustering within this sample may imply an elevated complexity of tasks with an oral modality, suggesting that this clinical group may have difficulties with verbal communication. Meanwhile, a dual-response task was implied to be the most complex within the WISC-V output, adhering to Guttman’s explanation of cognitive complexity, which suggests that the recruitment of more output processes results in heightened task difficulty (L. Guttman, 1954).

We thank Bond University and the Child Development Service, Gold Coast University Hospital, for supporting this research.