Rebecca J. Barall, MEd, CBIS, BCBA, LBA (NE, IA)
University of Nebraska Medical Center, Munroe-Meyer Institute

ASAT's Science CornerYou’ve just read about a promising new intervention for individuals with autism. It’s published in a reputable journal, shows strong results, and seems like it could help someone with autism you care about. But there’s one crucial issue to consider: the participants included in the study. Who was included? Not all study outcomes in autism research will apply equally to every individual. In other words, if the study’s participants don’t represent the diversity of the autism spectrum, its promising results may not translate to the person you have in mind. In this article, I will discuss how excluding individuals with autism who have the highest support needs, including those with profound autism, limits the applicability of study findings. I will also highlight why including individuals across the autism spectrum is critical for advancing science and practice.

Snapshots of Inclusion Across the Spectrum

The autism spectrum is broad, encompassing individuals with a vast range of abilities and support needs. However, most autism research has historically excluded individuals with the highest support needs from intervention studies (Stedman et al., 2019). For example, only about 11% of participants in autism research have IQ scores below 85 (Jack & Pelphrey, 2017). Additionally, approximately 30% of children with autism are minimally verbal, yet the literature on this population is limited, and definitions of “minimally verbal” vary across studies (Tager-Flusberg & Kasari, 2013). Minimally verbal children may be defined as those using some words but significantly fewer than expected for their age; for example, fewer than 5 words at 18 months and fewer than 50 words by around 30 months of age (Koegel et al., 2020). Notably, a 2019 meta-analysis of 301 studies found that only about 2% of participants in autism research were nonverbal or minimally verbal, highlighting a significant bias that excludes individuals with severe communication challenges (Russell et al., 2019). This suggests that a substantial portion of the autism population is frequently overlooked in research. Furthermore, Stedman et al.’s (2019) review of autism intervention studies found that the inclusion of individuals with profound autism in research declined over time, as demonstrated in studies conducted between 1991 and 2013. More current research is needed to determine if this worrisome trend has continued.

When key populations are underrepresented in autism research, it becomes difficult to determine whether interventions are truly effective for those who need evidence-based support (Shepard et al., 2019). Such exclusion can lead to “false negatives,” where treatments appear ineffective simply because they were not tested on the individuals most likely to benefit. Moreover, generalizing findings from studies that exclude subsets of the autism population to the entire autism population undermines both the validity and equity of research (Thurm et al., 2022). Ethical guidelines and historical practices in research have frequently prioritized the exclusion of vulnerable populations to prevent potential harm, especially for children, individuals with disabilities, and other groups considered at higher risk for adverse outcomes (Iacono & Carling-Jenkins, 2012). However, Northway (2014) compellingly raises the question of whether such efforts truly protect their interests or, instead, become another source of marginalization and disempowerment.

Why Are Some Subsets of the Autism Spectrum Left Out?

The underrepresentation of individuals with profound autism parallels broader gaps in participant diversity. A growing body of research shows that certain groups, such as autistic people of color, autistic women, autistic adults, individuals with a co-occurring intellectual disability, and those from under-resourced geographic areas or countries, are frequently excluded from intervention studies (de Leeuw et al., 2020; D’Mello et al., 2022; Malone et al., 2022; Steinbrenner et al., 2022; Thurm et al., 2022). These systemic exclusions across race, ethnicity, gender, age, intellectual ability, geographic region, and socioeconomic status limit the generalizability of findings to the full autism spectrum. As a result, evidence-based practices often reflect what works for a narrower segment of the population rather than the broader spectrum. Consequently, research findings must be interpreted with caution.

Factors Contributing to Research Gaps

Multiple factors contribute to the underrepresentation of certain groups in autism research. One major issue is the lack of standardized severity measures. Because studies define and measure “severity” differently, especially in measuring the communication abilities of individuals with profound autism, it’s difficult to compare results across studies (Stedman et al., 2019). Additionally, assessment challenges create further barriers. Many standardized assessments are not designed for individuals with profound autism, and while it is possible to tailor testing through sensory-friendly environments and rapport-building, these approaches are more resource-intensive and less commonly used (McKinney et al., 2021). This variability also makes it challenging to know the full extent to which individuals are included or excluded from research.

Recruitment practices also play a significant role, as researchers often include participants who are easier to engage and retain in studies, typically those who have relatively larger communication repertoires or require fewer behavioral supports to engage in research. As a result, individuals with the most complex needs are often excluded from studies (Maye et al., 2022).

Another important consideration is that funding priorities influence representation. Historically, funding mechanisms have often favored research with easily measurable outcomes, which has tended to select participants with fewer challenges and has deprioritized studies focusing on individuals with profound autism or autistic adults (Harris et al., 2021). However, in recent years, advocacy and funding from organizations such as the Profound Autism Alliance, National Council on Severe Autism, and the Autism Science Foundation have led the way in shifting funding priorities and supporting research that more fully includes individuals across the spectrum.

Caregiver and Stakeholder Take-Aways

As many studies exclude individuals with the highest support needs or from other underrepresented groups, caregivers and stakeholders can learn how to evaluate whether an intervention is likely to meet the unique needs of their child or loved one. To do this, caregivers and stakeholders can become more informed consumers of research by asking:

      • How does my child’s individuality shape their needs? As a consumer seeking information with a specific individual in mind, it would be beneficial to reflect on your child’s unique strengths, challenges, communication style, age, background, location, etc. Consider how these characteristics might influence how they respond to interventions and whether the research you are reviewing captures this diversity. This reflection helps you assess if the study findings are relevant and meaningful for your child’s distinct profile.
      • Who was included? Studies typically report demographic information about participants. Look for details like participant age, how they communicate, and any reported test scores, such as adaptive behavior or language measures. Understanding those scores can help you decide whether participants resemble your child. For practical guidance on interpreting standardized assessment scores in participant characterizations, see Connolly (2025).
      • Who may be missing? The target populations of some studies may or may not include groups that are historically underrepresented in autism research, such as minimally speaking individuals, adults with autism, or participants from diverse racial, linguistic, and ethnic backgrounds. Consider whether the study includes participants from groups that are often excluded and whether the findings are likely to apply to a learner with a behavioral and communicative profile like your child’s.
      • What outcomes were measured? Do the study’s goals (e.g., improving communication, increasing independence in daily living skills, reducing challenging behaviors) align with your child’s educational priorities? Even a well-designed study may not directly address your child’s specific goals. Also consider whether the research questions were evaluated only in highly controlled settings and whether the study and its findings have been evaluated for generalization (whether the skills or outcomes demonstrated in the study also occur in other contexts, such as your child’s school or home environment).
      • How to proceed when research seems to fit my child’s needs, or doesn’t?Some studies may include participants with profiles and educational needs that are similar to your child’s. In these cases, it may be easier to see how the study’s intervention could be applied in practice. In other cases, the participants, setting, or goals of the study may not align with your child’s needs and priorities. When this happens, the research may still serve as a useful reference. Consider consulting with your child’s clinical or educational support team to determine whether the intervention could be adapted for your child. These discussions can inform important decisions such as how to further individualize your child’s supports. Study results can be used and discussed in partnership with professionals to guide next steps and ensure that treatments remain grounded in evidence-based practice.

Toward Autism Research That Represents Everyone

When subsets of the autism spectrum are excluded from research, study findings can lose external validity. An intervention may be evaluated and found to be effective for a select subgroup, such as verbally fluent children with autism, but without including individuals with diverse developmental profiles and support needs, it is unclear whether the intervention will be effective across the full spectrum. To truly advance autism research and clinical practice that benefits everyone, applied researchers are encouraged to actively seek out and learn from the lived experiences of individuals with profound autism and their families. Understanding their unique challenges, strengths, and needs is essential to framing research questions that are both relevant and impactful. By integrating these perspectives more extensively into one’s research programs, research can move beyond narrow subgroups, and researchers can develop interventions and supports that genuinely address the diversity within the autism spectrum, ultimately improving outcomes for all.

Author Note

In this article, I use the term ‘minimally speaking’ to refer to individuals who use limited vocal speech to communicate, which may be preferred over ‘minimally verbal’ by members of the autism community (Bottema-Beutel et al., 2025). However, this article references both terms to accurately reflect the terminology used in cited works, while also incorporating the preferences of individuals within the autism community. These terms are often used interchangeably. Additionally, I use both person-first language and identity-first language throughout this paper to respect the diverse preferences within the autism community (Taboas et al., 2022).

References

Bottema-Beutel, K., Zisk, A. H., Zimmerman, J., & Yu, B. (2025). Conceptualizing and describing autistic language: Moving on from ‘verbal’, ‘minimally verbal’ and ‘nonverbal’. Autism, 29(6), 1367-1373. https://doi.org/10.1177/13623613251332573

Connolly, S. (2025). Science Corner: Interpreting standardized assessment scores in participant characterizations. Science in Autism Treatment, 22(8).

de Leeuw, A., Happé, F., & Hoekstra, R. A. (2020). A conceptual framework for understanding the cultural and contextual factors on autism across the globe. Autism Research, 13(7), 1029–1050. https://doi.org/10.1002/aur.2276

D’Mello, A. M., Frosch, I. R., Li, C. E., Cardinaux, A. L., & Gabrieli, J. D. E. (2022). Exclusion of females in autism research: Empirical evidence for a “leaky” recruitment-to-research pipeline. Autism Research, 15(10), 1929–1940. https://doi.org/10.1002/aur.2795

Harris, L., Gilmore, D., Longo, A., & Hand, B. N. (2021). Short report: Patterns of US federal autism research funding during 2017–2019. Autism, 25(7), 2135-2139. https://doi.org/10.1177/13623613211003430

Iacono, T., & Carling-Jenkins, R. (2012). The human rights context for ethical requirements for involving people with intellectual disability in medical research. Journal of Intellectual Disability Research, 56(11), 1122–1132. https://doi.org/10.1111/j.1365-2788.2012.01617.x

Jack, A., & Pelphrey, K. A. (2017). Annual research review: Understudied populations within the autism spectrum – current trends and future directions in neuroimaging research. Journal of Child Psychology and Psychiatry, 58(4), 411–435. https://doi.org/10.1111/jcpp.12687

Koegel, L. K., Bryan, K. M., Su, P. L., Vaidya, M., & Camarata, S. (2020). Definitions of nonverbal and minimally verbal in research for autism: A systematic review of the literature. Journal of Autism and Developmental Disorders, 50(8), 2957–2972. https://doi.org/10.1007/s10803-020-04402-w

Malone, K. M., Pearson, J. N., Palazzo, K. N., Manns, L. D., Rivera, A. Q., & Mason Martin, D. L. (2022). The scholarly neglect of black autistic adults in autism research. Autism in Adulthood, 4(4), 271-280. https://doi.org/10.1089/aut.2021.0086

Maye, M., Boyd, B. A., Martínez-Pedraza, F., Halladay, A., Thurm, A., & Mandell, D. S. (2022). Biases, barriers, and possible solutions: Steps towards addressing autism researchers’ under-engagement with racially, ethnically, and socioeconomically diverse communities. Journal of Autism and Developmental Disorders, 52(12), 4206–4211. https://doi.org/10.1007/s10803-021-05250-y

McKinney, A., Weisblatt, E. J., Hotson, K. L., Bilal Ahmed, Z., Dias, C., BenShalom, D., Foster, J., Murphy, S., Villar, S. S., & Belmonte, M. K. (2021). Overcoming hurdles to intervention studies with autistic children with profound communication difficulties and their families. Autism, 25(6), 1627-1639. https://doi.org/10.1177/1362361321998916

Northway, R. (2014). To include or not to include? That is the ethical question. Journal of Intellectual Disabilities, 18(3), 209–210. https://doi.org/10.1177/1744629514543863

Russell, G., Mandy, W., Elliott, D., White, R., Pittwood, T., & Ford, T. (2019). Selection bias on intellectual ability in autism research: A cross-sectional review and meta-analysis. Molecular Autism, 10(1), 9. https://doi.org/10.1186/s13229-019-0260-x

Shepherd, V., Wood, F., Griffith, R., Sheehan, M., & Hood, K. (2019). Protection by exclusion? The (lack of) inclusion of adults who lack capacity to consent to research in clinical trials in the UK. Trials, 20, 1–8. https://doi.org/10.1186/s13063-019-3603-1

Stedman, A., Taylor, B., Erard, M., Peura, C., & Siegel, M. (2019). Are children severely affected by autism spectrum disorder underrepresented in treatment studies? An analysis of the literature. Journal of Autism and Developmental Disorders, 49(4), 1378–1390. https://doi.org/10.1007/s10803-018-3844-y

Steinbrenner, J. R., McIntyre, N., Rentschler, L. F., Pearson, J. N., Luelmo, P., Jaramillo, M. E., Boyd, B. A., Wong, C., Nowell, S. W., Odom, S. L., & Hume, K. A. (2022). Patterns in reporting and participant inclusion related to race and ethnicity in autism intervention literature: Data from a large-scale systematic review of evidence-based practices. Autism, 26(8), 2026-2040. https://doi.org/10.1177/13623613211072593 (Original work published 2022)

Taboas, A., Doepke, K., & Zimmerman, C. (2023). Preferences for identity-first versus person-first language in a US sample of autism stakeholders. Autism, 27(2), 565–570. https://doi.org/10.1177/13623613221130845

Tager-Flusberg, H., & Kasari, C. (2013). Minimally verbal school-aged children with autism spectrum disorder: The neglected end of the spectrum. Autism Research, 6(6), 468–478. https://doi.org/10.1002/aur.1329

Thurm, A., Halladay, A., Mandell, D., Maye, M., Ethridge, S., & Farmer, C. (2022). Making research possible: Barriers and solutions for those with ASD and ID. Journal of Autism and Developmental Disorders, 52(10), 4646–4650. https://doi.org/10.1007/s10803-021-05320-1

Reference for this Article:

Barall, R. J. (2026). Science Corner: Who is missing from autism research – and why it matters. Science in Autism Treatment, 23(1).

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