What Are Intellectual Disabilities? - Definition, Characteristics & Types

Instructor: Chris Clause
In this lesson, you will learn to define intellectual disability as well as recognize factors associated with its cause. Following your completion of this lesson, you will have the opportunity to test your knowledge with a short quiz.


Formerly known as mental retardation, the term 'intellectual disability' refers to a wide range of cognitive and behavioral impairments associated with a significantly impaired intelligence level.

According the American Psychiatric Association (APA), intellectual disability is diagnosed after careful consideration across three domains: conceptual, social, and practical. All three domains interact with and impact one another, so the clinician must take into account each domain individually but understand how they interact as well.



Conceptual skills are oftentimes thought to include concepts related to intelligence - things like reading, writing, math, language, and memory. In a person with an intellectual disability, these areas will be significantly impacted. A standardized intelligence test is often used to assess these areas in addition to observation and other school-based assessments. Typically, a clinician will gather information from all of these sources in forming a diagnosis. An overall intelligence test score of 70, or two standard deviations below the general population's average score of 100, is used as the criterion level score for a person to be considered as having an intellectual disability.


Social skills are also highly impacted for people with an intellectual disability. Struggles with interpersonal skills and social judgment can have a significant impact on making friends and retaining social relationships. Additionally, difficulties with understanding and navigating the social world can impact confidence and self-esteem.


Practical skills (sometimes referred to as activities of daily living) are also significantly impacted in people with an intellectual disability. The cognitive skill deficits that are apparent in the conceptual domain not only impact academic areas like reading and math but also tasks associated with self-care. Challenges exist for people with an intellectual disability when it comes to things like shopping, money and time management, and making decisions about personal care.


Intellectual disability is the result of problems associated with the functioning of the central nervous system. In the case of genetically influenced intellectual disability, brain development does not occur properly, which results in conceptual, social, and practical skill impairments. Occasionally, trauma or injury to the brain during the key developmental periods of childhood can affect the central nervous system, resulting in significant impairments as well.

Many times, adults who acquire a brain injury or who are suffering from neurodegenerative diseases, such as dementia, will experience similar symptoms as are seen in people with an intellectual disability. It's important to note that while the symptoms may be similar, true intellectual disability is only diagnosed when significant skill impairments in conceptual, social, and practical skills manifest themselves during the developmental periods in childhood.

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