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From ADOS to ADOS-2

Since its launch in 2001, the Autism Diagnostic Observation Schedule has become the widely accepted gold standard for autism diagnosis. Now the ADOS has been expanded and refined with the arrival of the second edition (ADOS-2) in May this year. In this article we outline the structure of the original ADOS and look at the new features introduced with ADOS-2.

ADOS Background

ADOS is based on the triad of behaviours that characterise autism and autism spectrum disorders (ASDs) Ė namely difficulties with communication, social reciprocity and repetitive stereotyped behaviours - as defined in the major diagnostic systems of the American Psychiatric Associationís Diagnostic and Statistical Manual (DSM-IV), and the World Health Organisationís International Classification of Diseases (ICD-10).

Since its publication, the ADOS has increasingly been considered the gold standard observational instrument for the diagnosis of autism and ASDs. It involves direct observation of children and adults for whom an ASD is suspected, using one of four modules which differ according to the individualís expressive language ability and age.

ADOS Modules

Module One

Module One is for use with pre-verbal individuals and those with single-word speech. It comprises ten play-based activities designed to elicit behaviours indicating communicative and social intent and social engagement.

Module Two

Module Two is intended for use primarily with individuals using simple three-word phrases, as well as fluent children under age 3 years. It comprises several play-based activities, many overlapping with Module One, but with additional activities relevant for those with at least phrased-speech.

Module Three

This is for use with fluent children over age three years and adolescents. It comprises fourteen activities, which include some of the play-based activities used in Module Two, together with a number of conversational activities.

Module Four

Designed for use with older adolescents and adults, Module Four comprises fifteen activities (five of which are optional) that focus largely on conversational and social interchange.

For older adolescents and adults with single-word or phrased speech, the authors suggest use of Modules One or Two, as appropriate to communication level, but suggest some adaptation of materials and advise caution in the interpretation of results.

ADOS Scoring and Interpretation

Unlike in standard psychometric testing, the individual completing the ADOS is not generally scored in terms of how well s/he carries out a particular isolated activity. Rather, performance on each activity is used to contribute to scores in various functional domains related to communication, social reciprocity and stereotyped repetitive interests.

For classification and diagnostic purposes the ADOS-2 utilises an algorithm-based approach to maximise diagnostic accuracy. This means that specific items - which vary between modules - have been selected from the total item set for use in classification. The ratings assigned to these items are converted to algorithm scores listed at the back of the moduleís protocol sheet and then summed and compared to relevant cut-off points for autism, autism spectrum and non-spectrum. Specific item clusters contributing to these sums vary according to the childís language level in Module One and according to their chronological age in Module Two. Within Modules Three and Four contributing items are the same, regardless of age or ability.

ADOS-2

ADOS-2 is a revision of ADOS that has evolved from data gathered on its use, together with information from field-trials for new diagnostic guidelines which form the basis of the next edition of DSM (DSM-5). Publication of DSM-5 is expected in 2013.

ADOS-2 Modules

Administration of Modules One to Four remains functionally identical to ADOS.

ADOS-2 introduces a new Module called the Toddler Module, sometimes referred to as Module T. This is for children not yet using phrase speech and aged between 12 months and 30 months. The Toddler Module is designed to assess children with limited expressive language. It is based on the structure of Module One but incorporates developmental assumptions relevant to very young children at risk for ASD. It comprises eleven play-based activities, some of which also appear in Modules One and Two, together with additional activities more appropriate for the very young child.

ADOS-2 Scoring and Interpretation

Scoring and interpretation follows a similar form in all five ADOS-2 modules, but those familiar with ADOS will note some significant changes to previous scoring protocols.

A feature in ADOS-2 that was not present in the earlier edition, is the provision of Comparison Scores. These are designed to improve the usefulness of the instrument in

(a) comparing results of an administration with those of children with ASD of a similar age and language level, and

(b) in evaluating changes over time for an individual completing more than one assessment.

Currently, comparison scores are only available for children aged from 2 years to 14 years completing Module One or Module Two and children aged from 2 years to 16 years completing Module Three.

Diagnosis and Classification

As was the case with the ADOS, It is important to remember that ADOS-2 should only be used for diagnostic purposes in conjunction with information from various other sources. This should include details of the individualís developmental history together with observations in contexts other than the clinic, ideally in an environment that allows observation of the individualsí social behaviours. In this context, the ADOS-2 authors refer to instruments such as the Autism Diagnostic Interview Ė Revised (ADI-R) and the Social Communication Questionnaire (SCQ). Other instruments such as the Diagnostic Instrument for Social and Communication Disorders, (DISCO) are also useful sources of relevant information. Further information about the DISCO can be found on the NAS website.

For differential diagnosis on the autism spectrum it is also important to gather information on an individualís cognitive and language abilities. See the UK National Institute of Clinical Excellence (NICE) Clinical Guideline 142.