The meta-analysis extracted all EF data since ASD was introduced as a psychiatric diagnosis and showed consistent evidence of an overall moderate effect size of executive dysfunction in ASD. Individuals with a diagnosis of ASD performed on average significantly worse on EF in comparison with neurotypical controls. However, contrary to our prediction that individual EF subdomains would be differentially impaired, no significant differences in effect sizes were observed between these. Moderate effect sizes were observed for all of the established individual EF subdomains of interest. These findings suggest that there is relative equivalence of EF impairments in ASD across the constructs that were examined. This was further supported in this study by the largely homogeneous impact of most moderators on EF outcomes.

These findings are also consistent with the largely linear trajectory observed in the development of EF in ASD (see Supplementary Table 1) and recent trends in ASD research focussing on aberrant brain connectivity in predicting cognitive deficits and symptom severity in ASD.33, 34 A global impairment due to either under- or overconnectivity between brain networks broadly contributing to EF, as opposed to discrete anatomical deficits, could account for the lack of differences between subdomains of EF. The age comparison was only significant for the working memory domain. The age effect for working memory may relate to the developmental trajectory reported for some EF in neurotypical populations where performance may decline around puberty because of synapse reorganisation.35 Thus, the lack of significant difference in working memory observed in adolescents may reflect the underlying neural changes observed in this developmental period that may contribute to a decrease in EF performance in typically developing individuals. Differences therefore in this subdomain between the two groups may be least pronounced in this age range.

The generally smaller effect sizes on EF observed for the adult ASD group support other research that, either due to developmental maturity and/or increased use of compensatory strategies, adults with ASD perform better in EF than younger age groups, whereas residual executive dysfunction still persists. In addition, a smaller effect size between ASD and controls was observed when only one of the ADOS or ADI was used for diagnosis. Given the variability across ASD and recommendations for multifactorial assessment, use of a single diagnostic tool may result in a less severe cohort meeting much broader ASD criteria.

It was of interest to also note the small but significant moderating impact of Year of Publication on overall EF and for the domains of Concept Formation, Fluency and Planning that may reflect the broadening of the Autism Spectrum criteria over successive editions of the DSM since the diagnosis was first made in DSM-III.

It was hypothesised that the different diagnostic classifications of ASD may introduce variability between studies of EF, because of potential heterogeneity in cognitive function reflecting different classifications. However, our results failed to find differences in effect sizes between different diagnostic groups. This lends support to the recent focus on individual variability within the spectrum rather than between classification groups guiding EF outcomes.36

Similarly, an evaluation of the potential differences between different matching criteria did not reach significance, although the largest effect size was observed for matching based on chronological age. Differences in EF are likely to be more pronounced between experimental and comparison groups within the same age range when no other moderators such as IQ or mental age are taken into account.

Our findings on the clinical utility of EF measures show that the majority of EF measures did not achieve clinical utility in differentiating between ASD and typical controls, with mostly informant-based measures based on the BRIEF30 achieving absolute clinical marker criteria. This lends further support to the proposition that measures with ecological validity (that is, based on more representative environmental situations) may be more appropriate especially in clinical practice. Informant measures such as the BRIEF may offer greater clinical utility, but further investigations are needed to consider whether outcomes represent higher validity or might be influenced by demand or reporter characteristics. Based on the results of this study, however, the superior ecological validity of informant measures21 supports their use for circuitry-based models (Research Domain Criteria)37 and clinical staging models38 (matching developmental stage of impairment with clinical intervention and risk factors39) and for diagnostic and intervention frameworks. In addition, laboratory-based EF neuropsychological tests should be chosen based on feasibility and ease of use, given the relative equivalence of performance across domains. Taken together, these findings suggest that the focus of diagnostic and intervention measures needs to shift to a more ecologically and clinically valid framework while taking into account the likely individual differences within the spectrum.

A number of limitations may have influenced the findings of this study. The self- or informant-reported questionnaires were excluded from the majority of analyses given the significant differences in effect sizes compared against psychometric tests and experimental tasks. In addition, only accuracy-based measures were included in the analysis with all reaction time variables excluded given the direction and specification of the reaction time variable to EF can be unclear. Furthermore, we did not explore the impact that intraindividual variability within the spectrum may have on the observed findings. Finally, although we attempted to consider a comprehensive number of moderators, there remain a number of factors that may influence EF in ASD. These may relate to task characteristics (for example, task complexity, open-ended vs structured task format20) or participant characteristic including symptom severity, emotional states (for example, depression/anxiety) or comorbidities (for example, attention deficit hyperactivity disorder). Anxiety in particular has been noted to have a strong association with poor EF performance in ASD populations.40