Module 1 - Introduction to Mental Health Problems in People with a Dual Disability

Definitions of Intellectual Disability

If a person has a disability it means they find it more difficult or impossible to do normal tasks or things you would expect most people to be able to do. People identify different types of disability, sometimes based on the cause of the disability. For example someone may be described have a cardiac disability if they can’t walk very far before getting chest pain because of cardiac problems. At other times the disability is identified by the type of tasks or activities the person has difficulty in doing. In this way someone who is deaf could be described as having a hearing disability.   People with intellectual disability have difficulty in thinking and understanding (which is also called intellectual function or cognitive function.) Because of this difficulty they have problems in planning and undertaking a range of everyday tasks and for this reason they need extra support to get by. How much support depends on how severely their thinking ability is affected. This means that someone has an intellectual disability when their thinking is not working to a level that allows them to live independently and they need additional supports to live a normal life as possible. From a government point of view it is important to know who has an intellectual disability to decide who should receive services. For this reason intellectual disability has been described and defined in a way that enables people to decide if someone has an intellectual disability or not.   A person may be defined as having an intellectual disability if these three elements are present:

Below average intelligence


Deficits in adaptive functioning


Onset during the developmental period

Below are three of the most authoritative definitions of intellectual disability. Please use the back button on your browser to return to this page.  (American Association for Intellectual Disabilities) (page 176) (World Health Organisation ICD-10) (DSM-5 revision of the Diagnostic and Statistical Manual of Mental Disorders definition)  
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