What does it mean to have IDD and how common is it?

Intellectual and developmental disabilities (IDD)s begin in childhood and are lifelong disabilities that impact thinking and day-to-day activities. Here is some general information.

Is there a formal definition for IDD?

Although we encourage you to look into the various definitions for IDD, criteria generally include:

• Originated before the person reached 18 years of age
• Are likely to be life-long in nature
• Affect areas of major life activity, such as: personal care, language skills, learning abilities, the capacity to live independently as an adult, or any other prescribed activity.

How common is IDD?

Between 1 and 3 out of 100 people have an intellectual or developmental disability.

What causes IDD? Are people always born with an IDD?

For some people, IDD will be genetic, like Down syndrome. An IDD can occur due to damage to the brain caused during childbirth or when the person is quite young. Sometimes, the cause or “etiology” of the disability is not known.

Does IDD affect people in the same ways?

No. Everyone will be impacted by their IDD in a unique way. Some people may need more support in certain areas of life than other people.
There are probably some people in your agency for whom it was very clear from the time they were young children that they had an IDD, and for others it may not have been as obvious.

What about people with more severe levels of disability?

They may require help in all aspects of their day-to-day life and have medical issues related to their disability. Their ability to describe and report on their health may be particularly compromised, so having familiar people who know the person well is important.

What about people with more mild disabilities?

You may not always know with this second group whether they for certain have IDD as defined in legislation, or in medical diagnostic criteria. Even though the disabilities may be more subtle for this second group, we know that their lived experience can still be quite stressful for them and their families. Sometimes, having a more mild disability means additional challenges accessing services, which is stressful and can lead to poorer health outcomes. Having independence can also mean having less supervision and support, which can lead to making choices that can be harmful to one's health. Not understanding a disability can also lead to interpersonal tensions at home, at school, and at work, because expectations are not realistic, and supports are not in place. Individuals in this second group can have a host of physical and mental health issues that develop over time. If health care providers don't recognize that there is a disability, they might only see the health issues and wonder why the person is having difficulties explaining what is wrong and following through with treatment.