Email  |  Print

FAQ on the AAIDD Definition on Intellectual Disability

This FAQ provides a very general overview of the AAIDD systematic approach to the diagnosis, classification, and systems of supports for persons with intellectual disability as described in Intellectual Disability: Definition, Classification, and Systems of Supports (Schalock et al., 2010).  This approach is based on current knowledge regarding the etiology of intellectual disability and an ecological, multidimensional framework that is used as a basis for assessment, classification, and developing individualized supports.

Please note that the information in this FAQ is not meant to substitute for a reading of the text. A thorough and responsible understanding of the AAIDD system of diagnosing, classifying, and planning supports for persons with intellectual disability can only be obtained by reading the text in its entirety.

What is a disability?
The construct of intellectual disability belongs within the general construct of disability, which focuses on the expression of limitations in individual functioning within a social context and represents a substantial disadvantage to the individual. Intellectual disability has its genesis in organic and/or social factors. These organic and social factors give rise to functional limitations that reflect an inability or constraint in both personal functioning and performing roles and tasks expected of an individual within a social environment.

What is intelligence?
Intelligence is a general mental ability. It includes reasoning, planning, solving problems, thinking abstractly, comprehending complex ideas, learning quickly and learning from experience.

What is adaptive behavior?
Adaptive behavior is the collection of conceptual, social, and practical skills that have been learned and are performed by people in their everyday lives.  Although not a complete list, below are some of the commonly referred to adaptive behavior skills:
• Conceptual skills: language, reading and writing, and money, time, and number concepts.
• Social skills: interpersonal skills, social responsibility, self-esteem, gullibility, naïveté, following rules/obeying laws, actively avoiding being victimized, and social problem solving.
• Practical skills: activities of daily living, occupational skills, use of money, safety, health care, travel/transportation, schedules/routines, and use of the telephone.

What are supports?
Supports are resources and strategies that aim to promote the development, education, interests, and personal well-being of a person and that enhance individual functioning.

Why are supports important to people with intellectual disability?
The thoughtful planning and implementation of individualized supports leads to improved personal outcomes that may include more independence, better personal relationships, enhanced opportunities to contribute to society, increased participation in school and/or community settings and activities, and a greater sense of personal well-being/life satisfaction.

How can you determine what supports are needed?
Support needs is a psychological construct referring to the pattern and intensity of supports necessary for a person to participate in activities linked with normative human functioning. The pattern and intensity of supports needed by individuals with intellectual disability are best determined through a standardized support needs scale such as the Supports Intensity Scale ®.

What is the AAIDD definition of intellectual disability?
Intellectual disability is characterized by significant limitations both in intellectual functioning and adaptive behavior as expressed in conceptual, social, and practical skills, which are apparent prior to the age of 18.

The definition of intellectual disability above does not stand alone; the definition must be applied within a context based on five assumptions:
1. Limitations in present functioning must be considered within the context of community environments typical of the individual’s age peers and culture;
2. Valid assessment considers cultural and linguistic diversity as well as differences in communication, sensory, motor, and behavioral factors;
3. Within the individual, limitations often coexist with strengths;
4. An important purpose of describing limitations is to develop a profile of needed supports; and
5. With appropriate personalized supports over a sustained period, the life functioning of the person with intellectual disability generally will improve.

What factors must be considered in determining if a person has intellectual disability?
The operational definition of intellectual disability includes three key components: (a) the actual definition and the assumptions underlying it (described above); (b) the use of cutoff scores to establish the construct’s boundaries; and (c) the use of the assessment instrument’s standard error of measurement to establish a statistical confidence interval within which the person’s true score falls.

Cutoff scores establishing the boundaries for the construct of intellectual disability:
The criteria for significant limitations in intellectual functioning for a diagnosis of intellectual disability is an IQ score that is approximately two standard deviations below the mean, considering the standard error of measurement for the specific instrument used and the instruments’ strengths and limitations.

The criteria for significant limitations in adaptive behavior for a diagnosis of intellectual disability is performance that is approximately two standard deviations below the mean of either (a) one of the following three types of adaptive behavior (conceptual, social, or practical) or (b) an overall score on a standardized measure of conceptual, social, and practical skills. As with the intellectual functioning criterion, the assessment instrument’s standard error of measurement must be considered when interpreting the individual’s obtained score.

Standard Error of Measurement and Confidence Interval:
Any obtained score is subject to variability as a function of a number of potential sources of error including variations in test performance, examiner’s behavior, cooperation of the test taker, and other personal and environmental factors. Thus, the correct interpretation of a score is dependent upon the test’s standard error of measurement and the establishment of a statistical confidence interval within which the person’s true score falls.

• The standard error of measurement, which varies by test, sub-group, and age group, is used to quantify the above-reference variability and provide a statistical confidence interval around the obtained score within which the person’s true score falls.
• From the properties of the normal curve, a range of statistical confidence (i.e. confidence interval) within which the person’s true score falls can be established, with parameters of at least one standard error of measurement (66% probability) or of two (95% probability).

Does the change from Mental Retardation to Intellectual Disability mean that some people no longer have the disability?
No. The term intellectual disability covers the same population of individuals who were diagnosed previously with mental retardation in number, kind, level, type, duration of disability, and the need of people with this disability for individualized services and supports. Furthermore, every individual who is or was eligible for a diagnosis of mental retardation is eligible for a diagnosis of intellectual disability.

What are the causes of intellectual disability?
There are a number of causes of intellectual disability. Our understanding of the causes of intellectual disability focuses on the types of risk factors (biomedical, social, behavioral, and educational) and the timing of exposure (prenatal, perinatal, and postnatal) to those factors.

What role does IQ play in the AAIDD approach?
One of the three criteria required to be met for a diagnosis of intellectual disability is “significant limitations in intellectual functioning.”  Equal consideration should also be given to measures of intellectual functioning and adaptive behavior functioning in the diagnosis of intellectual disability.

How is the AAIDD approach different from other systems of defining and classifying intellectual disability?
In addition the AAIDD, two other major systems that are used to diagnose and/or classify persons with intellectual disability: the American Psychiatric Association’s Diagnostic and Statistical Manual (DSM-IV-TR, 2000) and the World Health Organization’s International Classification of Functioning, Disability, and Health (ICF-10, 2007).  Below are overviews of their diagnostic elements.

DSM-IV-TR (Mental Retardation)
According to the APA, the essential features of mental retardation are (a) significantly sub-average general intellectual functioning, (b) that is accompanied by significant limitations in adaptive functioning in at least two of the following skill areas: communication, self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academics, skills, work, leisure, health, and safety, and (c) the onset must occur before age 18 years.

The next edition, the DSM-5 will be released in 2013.  The proposed revision for this diagnostic category includes a change in the name to “intellectual developmental disorder” and criteria that are inconsistent with the AAIDD systemic approach.

ICF (Mental Retardation)
According to the WHO, mental retardation is a condition of arrested or incomplete development of the mind, especially characterized by impairment of skills manifested during the developmental period, skills which contribute to the overall level of intelligence (i.e., cognitive, language, motor, and social abilities), which can occur with or without any other mental or physical condition, and degrees of which are conventionally estimated with standardized intelligence tests.

The next edition of the ICF is expected in 2015.

Is the AAIDD approach compatible with the Individuals with Disabilities Education Improvement Act (IDEA)?
Yes, the 2004 Individuals with Disabilities Education Improvement Act defines mental retardation (the term intellectual disability isn’t used) as: “significantly subaverage general intellectual functioning, existing concurrently with deficits in adaptive behavior, and manifesting during the developmental period, that adversely affects a child’s educational performance.”

Why does the AAIDD approach place so much importance on the issue of classification?
The primary purposes of classification in the field of intellectual disability are grouping for funding, research, provision of services and supports, and communication about selected characteristics of persons and their environments.

Classification is used today for more than its historic purpose of simply grouping on the basis of IQ range bands or adaptive behavior limitation scores. Clinicians are currently being asked ‘classification questions’ such as whether the person diagnosed with intellectual disability is competent to be a witness, stand trial, consent to sexual activity, parent a child, be one’s own guardian, and/or retain custody.

In addition, other uses of classification information are found in the areas of research studies that evaluate the role that intellectual abilities, adaptive behavior, health, participation and context play in human functioning and personal outcomes; and approaches to resource allocation such as those based on assessed support intensity levels. These classification questions and expanded use of classification information require both thinking differently about the purposes of classification and approaching classification more broadly.

Professionals need to be familiar with the emerging trends in the development and use of multidimensional classification systems based on the multidimensionality of human functioning that involves: intellectual abilities, adaptive behavior, health, participation, and context. A multidimensional classification system based on these five dimensions is presented in Intellectual Disability: Definition, Classification, and Systems of Supports (Schalock et al., 2010).

Additional Resources

AAIDD approach to the diagnosis, classification, and systems of supports for people with intellectual disability

Visit the resource page to watch videos, view presentation archives, and link to journal articles.

The AAIDD Supports Intensity Scale ®

Visit the SIS Website  for information on the tool, research on its use, and training opportunities.