Viewpoint Expert opinions on trends and controversies in autism research.
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How do we measure autism severity?

by  /  20 March 2012
The Expert:

Raphael Bernier

Assistant Professor, University of Washington, Seattle

Missing measure: Should the severity of autism be defined by the intensity of a person’s symptoms or by his or her ability to function with them?

Just last week the parents of a young boy who I had diagnosed with autism asked me, “How severe is his autism?”

It was not the first time parents of children — or adults — with autism had posed that question to me. It is an important one, not only for families as they make sense of their child’s diagnosis and available treatment options, but also for the scientific community. How do we define autism severity, and is there a good measure of it?

But before we can measure autism severity, we need to come up with an acceptable definition of what it is. A literature search for peer-reviewed articles that include the terms ‘autism’ and ‘severity’ yields more than 1,300 results. But the definitions of severity vary among these studies as widely as the methods do.

Severity is often defined in terms of language ability, intellectual functioning or the presence of problematic behaviors such as aggression, all of which contribute significantly to an individual’s ability to function in social, academic and employment situations. However, they are not necessarily core features of autism as we currently conceptualize the disorder. If we define the severity of autism as the degree or intensity of autism itself, we need to direct our focus to the core features, namely social and communicative impairments, and repetitive or restricted interests and behaviors.

But even with the focus restricted to the core domains of autism, it remains unclear if severity should be defined in relation to the intensity of symptoms or an individual’s ability to function with them. And if severity is defined by intensity of symptoms, should it be measured by the total number of symptoms in the core domains, the degree to which the symptoms are expressed in these domains, or some combination of degree and number — with some symptoms carrying more weight than others?

There are challenges to each approach. It is easy to see how a child with mild symptoms in each of the core autism domains may seem ‘less severely’ impaired than a child with just a few key deficits that wholly prevent reciprocal social interactions. If severity is defined based on an individual’s ability to function, then common co-occurring impairments that are not necessarily core features of autism, such as cognitive deficits and challenging behaviors, need to be considered, because these factors can have a major impact on functioning.

Ultimately, who has more severe autism? Is it the child presenting with every textbook symptom linked to autism or the one with just a few core symptoms as well as associated challenging behaviors that significantly impact his or her day-to-day quality of life?

Clinicians and researchers are working on answering this question in several ways. As a scientist I’m driven to quantify and define the severity of autism. And although I strongly believe that a measure of severity has scientific utility by helping to elucidate the neurobiological mechanisms underlying the disorder, I do wonder if a single tool can ever successfully measure the severity of autism.

Multiple measures:

Researchers use several approaches to quantify autism severity, including rating scales such as the Childhood Autism Rating Scale1, the Gilliam Autism Rating Scale2 and the Autism Behavior Checklist3; questionnaires measuring autism traits and behaviors, such as the Autism Spectrum Quotient4, the Social Responsiveness Scale (SRS)5, the Pervasive Developmental Disorder Behavior Inventory6, the Autism Diagnostic Interview-Revised (ADI-R)7 and Autism Diagnostic Observation Schedule (ADOS)8; and measures of cognitive level, adaptive ability, language ability, and statistically derived combinations of them all9.

These approaches and instruments are incredibly valuable for characterizing autism; however, as highlighted by a 2009 study10, there are limitations to each approach. For example, many of the rating scales correlate strongly with an individual’s intelligence quotient (IQ), which reduces the focus on autism core symptoms. However, the SRS, which is less impacted by IQ, focuses primarily on social communication and does not include direct observation of the child.

Summary scores on the ADI-R have often been used as severity metrics for coreautism symptoms, but the ADI-R was not developed as a measure of severity. For example, higher scores generally indicate greater impairment, but non-verbal children are not administered a portion of the test, restricting the utility of the communication domain. Scores also vary based on the child’s IQ and age.

Similar complications arise when researchers use the ADOS summary scores. These are influenced by age and language level, which determine which version, or module, of the test is administered, limiting the ability of the ADOS to generalize across individuals.

The newest approach, a calibrated severity score10 that is based on raw ADOS scores, attempts to provide a standardized, clinician-based metric that controls for language ability and age when determining autism severity. It provides a promising approach that addresses many of the drawbacks of the other measures. But it is still too early to determine its usefulness in clinical settings and how effective it will be at providing insight into the underlying genetic and neurobiological features of autism.

Despite its untested status, I believe that a measure such as the calibrated severity score that accounts for a range of contributing factors is the appropriate approach to take. Specifically, a measure that controls for the contribution of age, language and cognitive ability; incorporates objective measures of observed behavior; includes measures of rarer behaviors that are most accurately reported by caregivers; and acknowledges challenging behaviors on a scale with variability and good psychometric properties should be the goal.

Crucial context:

These measures have significantly advanced our understanding of autism, although a precise characterization of severity has remained elusive. This is to be expected, given the fact that the disorder changes during development and is very heterogeneous. The measures are also used in multiple contexts, varying from clinical to research settings. It may be that the definition of autism severity, and how we measure it, should also vary across these contexts.

Given the diverse symptoms of children with autism, a clear understanding of the features of the disorder, including language ability, cognitive ability, medical complications and other behaviors such as aggression, self-injury and the tendency to wander away from caregivers, is needed to fully characterize the functioning level for any individual.

These qualifiers may prove more relevant to parents or clinicians because they can impact functioning as much, if not more, than the core autism symptoms. Better knowledge of how these related symptoms interact with core autism symptoms is critical to advancing our understanding of autism severity and to adapting diagnostic and clinical services accordingly. It is also crucial for helping to define the phenotype and for assessing treatment outcomes.

By contrast, given the underlying heterogeneity of autism, the focus on core impairments to the exclusion of associated challenges may help pinpoint the disorder’s disease-causing pathways. When studying the genetic and neurobiological contributions to autism, quantifying autism severity based on the presence and degree of core autism symptoms, rather than on impact on functioning, may be more relevant.

I am confident that in the not-too-distant future we’ll have a universal definition, or definitions, of autism severity. Perhaps we will have one that is based on core symptoms, a second one defined by functioning and maybe even a third definition that reflects the disorder’s societal or financial impact.

In order to get there, we as scientists, clinicians and parents need to understand more about the contributions and interactions between associated symptoms and core symptoms. We also need to build on the gains we’ve made using existing measures of severity and to consider autism severity as a function of the context in which we define it.

Although a severity metric can help evaluate treatment progress and guide planning, I’m not sure I want to be able to answer the question the parents in my office asked me last week. I’d rather be able to answer the question behind the question: “What can we expect for our child?” and to say, “We know what caused your son’s autism and we know what we can do to help you with the concerns you and he have.”

Raphael Bernier is assistant professor of psychiatry and behavioral sciences at the University of Washington in Seattle.


1: Schopler E. et al. (2010). Childhood autism rating scale, second edition (CARS2). Los Angeles, CA: Western Psychological Services.

2: Gilliam J. (1995). Gilliam autism rating scale. Austin. TX: Pro-Ed.

3: Krug D. et al. J. Child Psychol. Psychiatry 21, 221–229 (1980) PubMed

4: Baron-Cohen S. et al. J. Autism Dev. Disord. 31, 5-17 (2001) PubMed

5: Constantino J.N. (2002). The social responsiveness scale. Los Angeles, CA: Western Psychological Services

6: Cohen I.L. et al. J. Autism Dev. Disord. 33, 31-45 (2003) PubMed

7: Lord C. et al. J. Autism Dev. Disord. 24, 659-685 (1994) PubMed

8: Lord C. et al. J. Autism Dev. Disord. 30, 205-223 (2000) PubMed

9: Spiker D. et al. Am. J. Med. Genet. 114, 129-136 (2002) PubMed

10: Gotham K. et al. J. Autism Dev. Disord. 39, 693-705 (2009) PubMed

16 responses to “How do we measure autism severity?”

  1. Bob Castleman says:

    Thank you for your insightful article.

    As one recently diagnosed ASD, at age 52, no less, I have pondered this idea of severity. By all outward appearances, I am not severely impaired. But, I as reported by a parent, my IQ tested 4+ standard deviations above normal at around age 5. Yet I stumbled through school and ended up working in a series of low paying, dead end jobs. I attempted college 3 times, nearly completing a computer science degree, landing my first entry level “real” job at age 42 in I.T., a full 20 years past the normal freshly minted college graduate in Computer Science. Even then, the struggle to maintain employment has been daunting, and my career trajectory has been flat, regularly having opportunities passing me by in favor of more socially competent individuals.

    This brief synopsis begs the question, how severe is my impairment? Is simply surviving, undiagnosed and without typical autism interventions enough to say that I am mildly autistic? Or is the fulfillment of one’s potential also part of the measure of severity? It is not an easy question.

  2. Sunshine says:

    It’s *kinda* an easy question. You do not have to be wildly successful in order to be considered able bodied. My son is autistic, my dad is obviously an Aspie, and I certainly have autistic qualities. I remember struggling through certain aspects of school and a lot of things from my childhood make a LOT more sense now that I understand autism. But I don’t have a lot of the core features of autism. I’ve struggled to live independently and I’m nearing 30. I’m not autistic. I’m not disabled. Autistic traits certainly affected my ability to move upward in many careers- but that can be true of an NT’s temper or an NT’s inability to play nice with others, as well. It can be about not being able to work more than 8 hours effectively, or bad leadership skills. In the above case, it sounds like you ARE able to hold down employment, but your personality makes it difficult for you to score promotions. That’s just life; not really disability.

  3. K.I.M. says:

    Sorry “Sunshine”, just the ability to hold down a job for a year or two does not denote success. Quality of life is extremely important, as is one’s ablility to hold down a meaninful job and contribute to society as fully as possible are also important. Let’s face it, if a person is stymied and cannot hold down a minimum wage job for more than a year before having to leave because other employees won’t accept their “quirks”, would it not be better to have that person counselled and trained to allow them to work better with others so that they can be more productive and therefore earn a better wage, pay more taxes and take less from and even contribute to society? Would it also not be worth the time and effort to educate the other workers that these “quirks” are no less offensive or controllable than the issues a blind person or someone in a wheelchair might present. Most people would hold a door open for someone with a cane or in a wheelchair, but have no patience for someone who stutters or cannot hold a conversation for more than a few minutes.

    The whole point of neurodiversity is that ‘everyone’ is given the opportunity to become the person they wish to be and not be held back, bullied, mocked or otherwise be dismissed as being an incomplete or incapable person.

  4. andrew says:

    my sons level benjamin was 39 how severe is that
    his twin brother andrew jr was 47 how severe is that

  5. Amanda Feldmiller says:

    Also, as a parent there are days when I would describe my son’s autism as severe and other days that I hardly even notice it. Some days he seems so “normal” or he will converse in a way that he had not before or do something I have never seen him do before and I always think “THIS IS PROGRESS.” And then the next day he will want to speak nonsense, talk repeatedly about labels on toys and I will think, “maybe he does have severe autism.” I get the feeling that his function level fluctuates at school too–sometimes he is high functioning, sometimes low and sometimes severe. At the beginning of pre-school his teacher labeled him as “severe” from the acan test. At the end of the year she said things like “he’s not as severe as I thought he was.” She advised his summer school teacher, “He is very smart but he will try hard some days for you to think otherwise.” I don’t know what to make of his severity level. It is scary and I always second guess myself. To me, his autism fluctuates wildly and I wish I could pin point what makes the good days so high functioning.

  6. Anil Kumar says:

    Hi Amanda,

    Our son is awaiting diagnosis. His behaviour is similar to you kids : one day he shows signs of improvement (vocabulary, social interaction, motor skills)… other days all disappear… not sure how to rate him on CARS-2.

    • MomofASDson says:

      What many don’t understand is when a child with ASD wanders off or has a diagnosis and
      Is I supervised /or these kids are not behaving like society sees fit the state can and will snatch them
      Up and put them in foster care or group homes where they get physically and sexually
      Abused . I had a cop tell me if I can’t learn to control him , his inappropriate words etc the
      States going to take him! People thinking it’s sheltering don’t know what the dancers of
      A diagnosed child under 18 being “unsupervised ” the state calls it neglect . They throw our
      Kids in the mental hospitals and god forbid u disagree with them who get paid by
      The state by the way. They take your kid and try to terminate your rights for advocating
      For proper care that will someday allow for our child to become independent .
      Feel free to email me if anyone knows of any organizations or people to help parents help their
      Teen to be able to live independently safely .

  7. Owen Selkirk says:

    To all others who are ASD/AS or who’s loved ones are ASD.AS, people need to understand from a Autistic POV that people like me who are ASD need to realize Autism spectrum Disorder is not a disorder it is a difference yes people call it that but why people who have ASD/AS are not disorderly or disabled they are what I call gifted, not in the sense of better than others but gifted in the way of being able to excel in some areas and not do so well in others but what people do not realize is that ASD/AS can help you in area(s) that you excel in for me for example I’m very skilled in fixing cars,metal fabrication and other hands-on skills BUT I lack in my more literature and motor-skills, and I’m 16 and I am writing this for parents and other need to understand that all ASD/AS kids are not disabled or dumb and (pardon my language)retarded. People with ASD/AS are people have huge amounts of hidden potential but lack some skills they need to grow up and have a amazing future but what happens to most kids is that they are Sheltered by parents who are not as aware as most and they say that they need to protect them, The problem is that once your gone they will be in-trouble because of their dependence on you or others, what you must to combat this is to to get teachers, EA’s and others to work to help build you and your kids idea for a independent future to help them threw life’s hard challenges. PS if any one would like any more info about life inside a ASD/AS go look up Temple Grandin or just simply ask me for more info.

    Owen Selkirk 16 year old student with Autism.

  8. Jodie says:

    Hi am so new to all this and am basicall trying to find information and understand more about autism. My niece was diagnosed when she was two , she now eight years old and in mainstream school. She has a classroom assistant and is a ver bright and articulate child. What we find hard to understand is her chanllenging behaviour lately. Shes becoming disruptive in class, lashing out at home at times and having bad melt downs. She is a very loving child and shows affection but I cant help but worry as someone earlier stated will her behaviour continue to get worse. We have a dreaded fear of her becoming so aggressive when shes older that she would be placed into somewhere due to her mother not being able to manage her. I could never let this happen. We are just at a point where we dont know what to do or where else to turn. We are considering ABA therapy as a new approach.

  9. Nathan says:

    How to determine what type of autism my child has and find the right learning pattern to teach him or her.

  10. Mother of 3 children says:

    My daughter is unable to talk, read or write, needs assistance with everyday care, self harms if ANYTHING is not done in the ‘expected’ order. Has extremely challenging behaviour everyday. She cannot converse at all, any form of communication is very difficult, socially no idea how to behave. Is a danger to herself and others due to unawareness of dangers. She has been labelled ‘severe’ by her consultants. However, when I hear other parents or adults say x or y is severe or they label themselves as severe and yet can have a perfectly functioning conversation with others, can function in society I think they have NO IDEA what severe is. In their own little word not being able to move up the career ladder might be blamed on autism, having a bad day when perfectly able to function and communicate other days is NOT SEVERE AUTISM. I wish all those who think they are severe could walk in my daughters shoes for a day, live in her muddled, confused world, work out why she self harms, what is wrong… !

    • liss says:

      Well said, Mother of three xx

    • C says:

      You’re just one of those parents who dismisses anyone who isn’t their kid. Shut up. I AM just like your daughter, except I’m able to talk even though speech isn’t exactly easy for me. Stop talking like she’s a burden or that her life is horrible. You make it horrible by talking about her like you did in your comment.

  11. Tim says:

    Very well said, Mother of 3 children. I hear and see this baloney repeatedly by enablers looking for excuses. If their adult progeny did not pass their driving test, its because of their Severe Autism,.. yea, right!

  12. C says:

    Functioning labels are USELESS! I’m a 35 year old autistic adult and behaviorally I would register as severe, but I can speak although it’s not easy and that tends to make people say I’m “mildly” autistic.

    The truth is measuring severity is useless because it devalues the lives and worth of autistic people who can’t make their communications understood even though they’re fully competent.

    Presuming competence in nonverbal autistic people is the most important thing anyone can do, yet every fricken article here seems to treat them like they’re garbage.

  13. Claire Cameron says:

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