A Guide to the ADOS 2 for Autism Assessment


Written by Dr. Irma Campos, Ph.D., Licensed Psychologist

Autism Spectrum Disorder (also referred to as Autism) is an often misunderstood Neurodevelopmental Disorder that presents at an early developmental stage. Neurodevelopmental Disorders are defined as mental disorders that present in early development and are associated with social, academic/vocational, and physical impairments in functioning across settings (American Psychiatric Association, 2013). Autism Spectrum Disorder’s diagnostic features include nonverbal and verbal social-communication deficits significantly below expected level relative to an individual’s cognitive (or IQ) functioning. In addition, another key diagnostic feature of Autism Spectrum Disorder is the presence-at some point in development-of stereotyped or restricted behaviors, interests, or speech. Examples of include strong attachment to unusual interests (e.g., sensory aspects of toys) or rituals/routines. In order to meet criteria for Autism Spectrum Disorder, these symptoms must be associated with notable impairments (American Psychiatric Association, 2013). Because of the complexity and range of symptomatology, Autism Spectrum Disorder continues to be one of the most challenging mental disorders to diagnose. Effective and prompt diagnosis requires professionals (e.g., licensed psychologists) specialized in diagnosing this disorder with the recommended use of standardized assessments, such as the ADOS-2. The ADOS-2 assessment will be further discussed in detail in this article.

Approximately 1.7% of children by the age of eight are diagnosed with Autism Spectrum Disorder (ASD) in the United States (Maenner et al., 2016). This 2016 estimate was notably higher compared to 2014 prevalence estimates. Prevalence rate estimations only differed for Latino/a children, whereby slightly lower rates among this ethnic group were found. Indicative of racial health disparities, however, African American children diagnosed with ASD were less likely to receive an Autism evaluation by three years of age relative to White American children (Maenner et al., 2016). Autism was 4.3 times more prevalent among male than female children, which may be influenced in part by differences in gender socialization and evaluator bias. Nonetheless, early and equitable diagnostic processes are critical in order for children to receive adequate resources and treatment. Early identification and intervention, indeed, has been linked to improved outcomes for children diagnosed with ASD.

Importance of a Standardized Assessment

Diverse clinical profiles can be indicative of ASD. These diverse profiles can appear even more heterogenous due to comorbidities (co-occurrence with other disorders), which are quite common among individuals diagnosed with ASD. Notably, behaviors and symptoms may not be fully reported or observed during a standard clinical parent or client interview. A comprehensive evaluation (e.g., Autism-specific clinical interview, standardized assessment, and information from multiple raters) is required to diagnose ASD. Standardized, observational assessment and scoring processes can prove critical in effectively diagnosing ASD because they provide a more complete picture of symptoms and behaviors.

A standardized assessment aids in confirming the highly specific criteria of the Diagnostic Statistical Manual-Fifth Edition (DSM-5). A standardized process can also remove bias in the diagnostic process. Although most evaluators do not intend to exhibit biases in their diagnostic processes, cognitive biases can inevitably emerge. Some examples of cognitive biases that unconsciously occur include anchoring (i.e., focusing on one piece of information in the diagnostic process) and availability heuristic (i.e., focusing on recent diagnoses and overestimating the probability of that diagnosis occurring again) (See this link for more information on cognitive biases: https://www.cmpa-acpm.ca/serve/docs/ela/goodpracticesguide/pages/human_factors/Cognitive_biases/pdf/hf_common_cognitive_biases-e.pdf).

Standardized assessments have also undergone iterations to ensure adequate levels of reliability (i.e., consistency in results over time) and validity (i.e., measure of an assessment measuring what is supposed to measure). Reliability and validity measures are assessed by statistically analyzing clinical data with samples that should be as representative as possible of the general population in terms of demographic characteristics. Standardized assessments are administered in the same way each time in order to ensure reliability, validity, and reduction of biases.

ADOS-2 Background

The Autism Diagnostic Observation Schedule, Second Edition (ADOS-2) is both a standardized and observational assessment used to diagnose Autism Spectrum Disorder across age groups and language abilities from toddlers to adults (Lord, Rutter, DiLavore, Risi, Gotham, & Bishop, 2012; Lord, Luyster, Gotham, & Guthrie, 2012). The ADOS-2 is a revision of the ADOS. Five modules comprise the ADOS-2, and the module to be used is selected based on the individual’s chronological age and expressive language ability. Throughout the assessment, interactive tasks are administered to elicit behaviors that can reveal Autism symptomatology. The ADOS-2 includes presses, or planned social tasks, that facilitate situations in which specific behaviors are likely to occur (Lord et al., 2012). These tasks are part of the specific coding process within five general areas (Language & Communication; Reciprocal Social Interaction; Play/Imagination; Stereotyped Behaviors and Restricted Interests; and Other Abnormal Behaviors). The codes are converted to reach an algorithm score and used to complete a diagnostic algorithm. There are separate diagnostic algorithms for different modules.

ADOS-2 Research and Utility

Within the ADOS-2 manual, three samples were used to assess psychometric properties (relatability and validity) of the ADOS-2 (Lord, Rutter, DiLavore, Risi, Gotham & Bishop, 2012). Two forms of reliability (interrater and test-retest) were assessed for Modules 1-3, and results indicated acceptable Overall Total score reliability (from .87 to 96) for Modules 1-3. Regarding validity, as an example of one of the studies conducted, a replication study will be discussed. In this study, a statistical analysis (Exploratory Factor Analysis) replicated findings regarding the two primary ADOS-2 domains (Social Affect and Restricted Repetitive Behaviors). Regarding the ADOS-2’s ability to predict the disorder, another analysis (Logistic Regression) found that the Social Affect domain significantly predicted Autism diagnoses beyond the Autism Diagnostic Interview-Revised (Lord et al., 2012).

In terms of clinical utility, the ADOS-2 can serve multiple purposes, including aiding in the diagnostic process; informing specific treatment plans and goals; and assessing symptom changes and treatment progress over time. As previously noted, the ADOS-2 increases diagnostic accuracy in light of the complex presentations of Autism Spectrum Disorder. It can help confirm the presence of necessary diagnostic criteria by facilitating observation of behaviors deemed indicative of Autism.

The ADOS-2 can also identify individual growth areas and strengths. Because of the coding process, the ADOS-2 can provide specific information about a person’s performance within domains rather than simply examining total scores. As such, these findings can inform treatment plans and specific goals to target in treatment. In any course of treatment, it is usually beneficial to amplify strengths but also work on developing growth areas or deficits. Strengths and growth areas can vary from individual to individual so it is helpful to have an assessment that elucidates these individual differences.

Notably, the ADOS-2 can also be used to assess change over time, if a client’s symptoms need to be measured after treatment interventions are implemented. Indeed, after a period of treatment, such as Applied Behavior Analysis Therapy, it could be helpful to assess if an individual’s symptoms have improved in target areas.

The ADOS-2 can serve multiple clinical purposes, including aiding in effectively diagnosing Autism; facilitating treatment planning; and measuring treatment progress. Autism Spectrum Disorder diagnostic and treatment planning processes should not be taken lightly, as early intervention is key with this disorder. I urge parents, clients, and providers to reflect on the importance of incorporating a standardized assessment, such as the ADOS-2, in any Autism evaluation.


American Psychiatric Association. (2013). Neurodevelopmental Disorders. In Diagnostic and statistical manual of mental disorders (5th ed.).https://dsm.psychiatryonline.org/doi/full/10.1176/appi.books.9780890425596.dsm01

Lord, C., Rutter, M., DiLavore, P. C., Risi, S, Gotham, K., & Bishop, S. L.  (2012). Autism Diagnostic Observation Schedule, Second Edition (ADOS-2) [Manual: Modules 1-4]. Torrance, CA: Western Psychological Services.

Lord, C., Luyster, R. J., Gotham, K. & Guthrie, W. (2012). Autism Diagnostic Observation Schedule, Second Edition (ADOS-2) [Manual: Toddler Module]. Torrance, CA: Western Psychological Services.

Maenner MJ, Shaw KA, Baio J, et al. Prevalence of Autism Spectrum Disorder Among Children Aged 8 Years — Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2016. MMWR Surveill Summ 2020;69(No. SS-4):1–12. DOI:http://dx.doi.org/10.15585/mmwr.ss6904a1