# Autism Diagnostic Observation Schedule

The Autism Diagnostic Observation Schedule (ADOS) is a standardized diagnostic test for assessing autism spectrum disorder. The protocol consists of a series of structured and semi-structured tasks that involve social interaction between the examiner and the person under assessment. The examiner observes and identifies aspects of the subject's behavior, assigns these to predetermined categories, and combines these categorized observations to produce quantitative scores for analysis. Research-determined cut-offs identify the potential diagnosis of autism spectrum disorder, allowing a standardized assessment of autistic symptoms.
The Autism Diagnostic Interview-Revised (ADI-R), a companion instrument, is a structured interview conducted with the parents of the referred individual to cover the subject's full developmental history. The ADI-R has lower sensitivity but similar specificity to the ADOS. The ADI-R and ADOS are both considered gold standard diagnostic tests for autism. However, neither of these tests are required by the DSM-5 for an autism diagnosis.

## Development and History
### ADOS

The original ADOS was created by Catherine Lord, Michael Rutter, Pamela C. DiLavore and Susan Risi in 1989. The protocol consisted of 8 tasks meant to assess the individual’s social and communicative behaviors. Behaviors were rated on the following scale:
* (0) within normal limits
* (1) infrequent or possible abnormality
* (2) definite abnormality
Some ratings could also be assigned a rating of 7, indicating observed behaviors not otherwise specified.

### PL-ADOS

In response to the need for diagnostic tools for autism in younger children, researchers developed the Pre-Linguistic Autism Diagnostic Observation Schedule (PL-ADOS). The PL-ADOS adapted the content and format of the original ADOS to rely less on verbal communication. It consisted of 12 tasks, retaining only the free/unstructured playtime from the original ADOS and adding new activities designed to be less dependent on speech.

### ADOS-G

In 2000, Lord and her colleagues introduced the ADOS-Generic (ADOS-G) to assess a broader developmental range of individuals. The ADOS-G introduced a modular format, allowing different protocols to be used depending on developmental and language factors. It became commercially available in 2001 through Western Psychological Services.

### ADOS-2

The second edition, published in 2012, included updated norms, improved algorithms for Modules 1 to 3, and a new Toddler Module (T) for assessing children aged 12 to 30 months. The scoring algorithm was also revised to align with the recent changes in the DSM-5 diagnostic criteria. While the ADOS-G had separate sections for social and communication behaviors, the ADOS-2 combined these into a single domain to represent social affect, and added a new domain to assess restrictive and repetitive behaviors (RRB).

## Method

The ADOS consists of a series of structured and semi-structured tasks that generally takes 30-60 minutes to administer. During this time, the examiner provides a series of opportunities for the subject to show social and communication behaviors relevant to the diagnosis of autism. Each subject is administered activities from the module that corresponds to their developmental and language level. The ADOS should not be used for formal diagnosis with individuals who are blind, deaf, or otherwise seriously impaired by sensory or motor disorders, such as cerebral palsy or muscular dystrophy.
Following task administration and observation coding, a scoring algorithm classifies the individual with autism, autism spectrum disorder, or non-spectrum. The toddler module algorithm yields a "range of concern" rather than a definite classification.

## Modules
### Toddler module

The toddler module is appropriate for children 12–30 months who use little to no phrase speech and are able to walk independently. This module consists of eleven primary activities:
* Free play
* Blocking toy play
* Response to name
* Bubble play
* Anticipation of a routine with objects
* Response to joint attention
* Responsive social smile
* Anticipation of social routine
* Functional and symbolic imitation
* Bath time
* Snack

### Module 1

Module 1 is appropriate for children 31 months and older who use little or no phrase speech. This module consists of ten activities:
* Free play
* Response to name
* Response to joint attention
* Bubble play
* Anticipation of a routine with objects
* Responsive social smile
* Anticipation of a social routine
* Functional and symbolic imitation
* Birthday party
* Snack

### Module 2

Module 2 is appropriate for children six years old or younger who speak in phrases but have not yet developed fluent verbal language. This module consists of fourteen activities:
* Construction task
* Response to name
* Make-believe play
* Joint interactive play
* Conversation
* Response to joint attention
* Demonstration task
* Description of a picture
* Telling a story from a book
* Free play
* Birthday party
* Snack
* Anticipation of a routine with objects
* Bubble play

### Module 3

Module 3 is appropriate for children or young adolescents who are verbally fluent. This module consists of fourteen activities:
* Construction task
* Make-believe play
* Joint interactive play
* Demonstration task
* Description of a picture
* Telling a story from a book
* Cartoons
* Conversation and reporting
* Emotions
* Social difficulties and annoyance
* Break
* Friends, relationships, and marriage
* Loneliness
* Creating a story

### Module 4

Module 4 is appropriate for older adolescents and adults. While similar to module 3, module 4 relies more heavily on questions and verbal responses rather than non-verbal actions observed during play. This module consists of ten to fifteen activities. Activities marked by an asterisk are optional:
* Construction task*
* Telling a story from a book
* Description of picture*
* Conversation and reporting
* Current work or school*
* Social difficulties and annoyance
* Emotions
* Demonstration task
* Cartoons*
* Break
* Daily living*
* Friends, relationships, and marriage
* Loneliness
* Plans and hopes
* Creating a story

## Diagnostic accuracy

The social communication difficulties that the ADOS and ADOS-2 seek to measure are not unique to ASD; there is a heightened risk of false positives in individuals with other psychological disorders. In particular, an increased false positive rate has been observed in adults with psychosis; while case reports indicate that such false positives may also occur in cases of childhood-onset schizophrenia, which is an exceptionally rare entity with a frequency of 1 in 40000. There is evidence that adults with schizophrenia demonstrate an increased incidence of autistic features compared to the general population, resulting in higher ADOS scores, though schizophrenia patients also experience positive symptoms of psychosis (e.g. hallucinations, delusions, formal thought disorders). A 2016 study found that 21% of children with a diagnosis of ADHD (and without a concurrent diagnosis of ASD) scored in the autism spectrum range on the ADOS total score. False positives have also been found in school-age subjects who have high anxiety or trauma-related disorders; in these cases, the ADOS-2 scores related to repetitive and restrictive behaviors (RRB) are usually lower than typical for ASD.
A 2018 Cochrane systematic review included 12 studies of ADOS diagnostic accuracy in pre-school children (Modules 1 and 2). The summary sensitivity was 0.94 (95% CI 0.89 to 0.97), with sensitivity in individual studies ranging from 0.76 to 0.98. The summary specificity was 0.80 (95% CI 0.68 to 0.88), with specificity in individual studies ranging from 0.20 to 1.00. The studies were evaluated for bias using the QUADAS-2 framework; of the 12 included studies, 8 were evaluated as having a high risk of bias, while for the remaining four there was insufficient information available for the risk of bias to be properly evaluated. The authors could not identify any studies for the ADOS-2; the scope of the review was limited to preschool age children (mean age under 6 years), which excluded studies of Modules 3 and 4 from the meta-analysis. One included study examined the additive sensitivity and specificity of the ADOS used in combination with the ADI-R; that study found an 11% improvement in specificity (compared to ADOS alone) at the cost of a 14% reduction in sensitivity; however, due to overlapping confidence intervals, that result could not be considered statistically significant.