The Autism Diagnostic Observation Schedule. Second Edition (A.D.O.S.-2)

The Autism Diagnostic Observation Schedule,  Second Edition (A.D.O.S.-2), is the “gold standard” for diagnosing Autism Spectrum Disorders – or ruling them out – at any age and developmental level, irrespective of language skill or level of functioning. It can be quickly and reliably administered to subjects ranging from children as young as 18-months-old through adolescence and adulthood. The A.D.O.S.-2 is widely used in research and in academic centres around the world. In fact, it has become the leading tool used by clinicians when an Autism Spectrum Disorder (A.S.D.) is suspected. The A.D.O.S.-2 assesses behaviour, communication, social interaction, play, and the imaginative use of materials for individuals suspected of having A.S.D.

The A.D.O.S.-2 has exceptional sensitivity and specificity: These are terms used by researchers to evaluate the accuracy of test results. Sensitivity refers to how accurate assessments are in correctly identifying the conditions they were designed to detect. Reportedly, the latest version of the A.D.O.S. achieved a sensitivity rating of 95%. Therefore, the A.D.O.S.-2 yields a correct diagnosis 95% of the time. Only 5% of test administrations yield “false negatives,” in which Autism Spectrum disorders are missed. Many other tests commonly used to assess Autism Spectrum Disorders in toddlers, including some of the most highly-regarded, are significantly less sensitive than the A.D.O.S.-2. For example, the Checklist for Autism in Toddlers (C.H.A.T.) and the Early Screening for Autistic Traits (E.S.A.T.) miss as many of 50% of cases that are later correctly diagnosed.

Specificity relates to how well a test differentiates its target condition (Autism Spectrum Disorder, in this case) from others that may be present. Again, the A.D.O.S.-2 was found to have an extremely high specificity of 95%.  This means that individuals with difficulties resembling A.S.D. but with other underlying causes will be misdiagnosed only about 5% of the time.  In other words, there are far fewer “false positives” than with other tests. The A.D.O.S.-2 defined the “boundary between autism spectrum disorder and milder disorders with overlapping symptoms, like A.D.H.D., nonverbal learning disability and speech and language disorders.” It is very unusual for tests to have such high sensitivity and specificity: Leading Autism Researcher Nestor Lopez-Duran described the A.D.O.S.-2 as “The most reliable and valid diagnostic instrument available.”

Closely related to sensitivity is the statistical concept of internal validity, which has been established for the A.D.O.S.-2. This means that clear causal links have been shown to exist between Autism Spectrum Disorders and the traits identified by the test.

The A.D.O.S.-2 also displays a high level of test-retest reliability – meaning it is highly likely to yield the same results in repeated administrations over time.

 The A.D.O.S.-2 has demonstrated very high inter-rater reliability, exceeding 84%. This means that if two or more trained testers observing the same child are scoring independently they will reach the same conclusions more than 84% of the time. This is significant because test results can be influenced by extraneous factor (e.g., where and when a test is given, the child’s emotional state, his or her rapport with the person giving the test, and the clinician’s subjective impressions of the child). The A.D.O.S.-2 offers greater objectivity than most measures.