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What’s the Difference Between Intellectual and Developmental Disabilities?

What’s the Difference Between Intellectual and Developmental Disabilities?

There is a fairly large category of disability referred to as intellectual and developmental disabilities (IDDs). It’s used to describe a broad number of conditions, including Down syndrome, autism spectrum disorders (ASDs), fragile X syndrome, cerebral palsy, muscular dystrophy, spina bifida, attention-deficit disorder (ADD) and attention-deficit hyperactivity disorder (ADHD), fetal alcohol spectrum disorders, various sensory and learning disorders, language and speech disorders, kernicterus, tourette syndrome, and others.

Exactly which conditions are included and, in fact, the precise overarching definition of intellectual and developmental disabilities—can vary depending on the source. However, IDDs are generally described as conditions that are usually present from birth that impede a person’s physical, mental, and/or emotional development. In addition, when applying for services, there are categories of intellectual disabilities grouped by the IQ level of intellectual disability and time of onset may be a qualifying factor.

When people are newly learning about IDDs, one of the most common questions that arises is: What’s the difference between intellectual and developmental disabilities? So, here’s a quick look at the answer.

About Developmental Disabilities

Developmental Disabilities is the larger category and includes Intellectual Disabilities as one of the developmental disabilities.  All intellectual disabilities are technically developmental disabilities, but all developmental disabilities are not intellectual disabilities. Developmental disabilities is an umbrella term that includes those typically present from birth or childhood that can affect any combination of a person’s physical, cognitive, and/or emotional development.

A condition like cerebral palsy, which has symptoms and complications that are primarily physical in nature, is an example of a developmental disability; it would not be considered an intellectual disability.

About Intellectual Disabilities

Intellectual disabilities are more specifically those in which a person’s cognitive abilities are impaired (and often include impaired emotional development). Many, but not all  conditions that are classified as intellectual disabilities have physical elements as well. Down syndrome, fragile X syndrome, and autism spectrum disorders are examples of intellectual disabilities.

There are three primary criteria for intellectual disability:

  • Significant limitations in intellectual functioning
  • Significant limitations in adaptive behavior
  • Onset before the age of 18

The first of these criteria, significant limitation in intellectual functioning, is determined by an IQ test. Intellectual functioning includes processes like learning, reasoning, and problem solving; an IQ score at or below 70 would be considered to meet this criteria.

Other tests are used to evaluate adaptive behavior, which includes three types of skillsets:

  • Conceptual skills (language and literacy; money, time, and numerical concepts; self-direction)
  • Social skills (interpersonal skills, social responsibility, self-esteem, gullibility, social problem solving; the ability to follow rules, obey laws, and avoid being victimized)
  • Practical skills (personal care and other activities of daily living, occupational skills, healthcare, travel/transportation, schedules and routines, safety, use of money, etc.)

A person with intellectual disabilities can learn skills to achieve daily living activities, occupational skills, schedules, routines, and even work skills with more frequent and repetitious training and practice.  All people with and without disabilities have limitations.  People with disabilities have more limitations and some cannot be overcome.  The goal should be to achieve skills with training and practice to limit the disabilities the best we can and identify the disabilities we cannot and get supports to help with those disabilities.  You know that feeling of accomplishment and success?  Why would you not encourage your person with disabilities to feel that and own that feeling?   Allowing our loved ones to live as independently as possible is the greatest give we can give them and as hard as it is to let go, it is the greatest give you can give yourself…


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