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Intellectual and Developmental Disabilities

This guide aims to provide background on IDD and the many contributing factors/diagnoses, as well as resources for student/faculty researchers and relevant organizations to be aware of.

What are Intellectual and Developmental Disabilities?

Intellectual and Developmental Disabilities (commonly shortened to IDD) are defined in many different contexts, depending on many different factors. There can be several different causes for intellectual and developmental disabilities, and the vast majority of individuals impacted by IDD don't know the direct cause of their condition (CDC, 2021).

Depending on the organization you ask, there are different (and sometimes competing) understandings in how we define and approach IDD. Take a look at some example definitions below.

"Intellectual disability is a condition characterized by significant limitations in both intellectual functioning and adaptive behavior that originates before the age of 22."

"Assessments must also assume that limitations often coexist with strengths in a person, and that an individual's level of life functioning will improve if appropriate, personalized supports are provided over a sustained period."

American Association on Intellectual and Developmental Disabilities

"Intellectual disability is a below-average cognitive ability with three (3) characteristics:

  • Intelligent quotient (or I.Q.) is between 70-75 or below
  • Significant limitations in adaptive behaviors (the ability to adapt and carry on everyday life activities such as self-care, socializing, communicating, etc.)
  • The onset of the disability occurs before age 18."

The Arc

"Intellectual disability means significantly subaverage general intellectual functioning, existing concurrently with deficits in adaptive behavior and manifested during the developmental period, that adversely affects a child’s educational performance. The term “intellectual disability” was formerly termed “mental retardation.”

Individuals with Disabilities Education Act

"Intellectual disability starts any time before a child turns 18 and is characterized by differences with both:

  • Intellectual functioning or intelligence, which include the ability to learn, reason, problem solve, and other skills; and
  • Adaptive behavior, which includes everyday social and life skills.

The term "developmental disabilities" is a broader category of often lifelong challenges that can be intellectual, physical, or both."

National Institute of Child Health and Human Development

"Intellectual disability is a term used when there are limits to a person’s ability to learn at an expected level and function in daily life. Levels of intellectual disability vary greatly in children."

Centers for Disease Control and Prevention