This page provides brief answers to some frequently asked questions (FAQs) about intellectual disability (ID) and the 12th edition of the AAIDD manual. The 12th edition of the AAIDD manual was published in 2021.
ID is a developmental disability. Each person with ID will have their own strengths and weaknesses and will require lifelong supports of a personalized level, intensity, and duration to optimally engage in their environment.
Clinical judgment plays an important role in all aspects of the determination of ID. As described in more detail in the Manual, a clinician will consider evidence concerning each of the three diagnostic criteria, including any potential sources assessment or measurement error:
As described in more detail in the Manual, all test results must be interpreted within the context of their administration and any potential sources of testing error. In making a determination of ID, evidence in addition to test scores will inform the diagnostician's clinical judgment of the person's overall functioning.
For more information on the diagnosis of ID, consult the AAIDD manual. The "Twenty Questions" document on this page also contains useful information concerning diagnosis, classification, and clinical judgement.
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There is no dispute that ID originates during the developmental period, but there have been some minor inconsistencies among the various perspectives (e.g., etiological, functional, cultural, administrative) on the age at which the developmental period ends. AAIDD acknowledged In prior editions of its Manual that some societies and contexts define the developmental period differently than was described in those editions.
In its 12th edition of the Manual, AAIDD defines the end of the developmental period as age 22 based on contemporary research that has shown that important brain development continues into our 20s. Additionally, and as discussed further in the Manual, this age of onset is also consistent the standards used for a diagnosis of ID in the DSM-5 and the ICD-11 and for service eligibility by the US Social Security Administration.
The change in the operational definition of developmental period is not expected to impact prevalence rates because the vast majority of diagnoses of ID are--and will continue to be--made in early childhood; however, this change will enable the accurate diagnosis of the small percentage of individuals who are identified nearer to the end of the developmental period.
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