Information about intellectual disability: what is it? Effects of intellectual disability.

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What is intellectual disability?

A Definition

    Intellectual disability is a disability that:
  • occurs in the developmental period and is characterised by sub-average intellectual functioning
  • IQ is assessed as 70 or under
  • deficits in at least 2 areas of adaptive behaviour, i.e. communication, self care, home living, social skills, self direction, leisure and work, learning

In clinical terms intellectual disability is often defined in terms of the severity of the condition:

Clinical term Percentage IQ
MILD intellectual disability 75 55 - 70
MODERATE 20 30 - 55
SEVERE 5 under 30

The use of the word “MILD” suggests a disability of little consequence. This is far from accurate.

  • A person with mild intellectual disability will have significant difficulty managing their lives effectively without support and training
  • Many people with mild intellectual disability live independently but struggle with many everyday issues
  • Many try to cover up their difficulties
  • Many receive no assistance
  • A person with mild intellectual disability would have great difficulty in understanding what is happening at court and what is required of them (eg bail conditions, AVO orders) without assistance

Intellectual disability is best assessed by a psychologist and some people with intellectual disability may have more than one disability. For example some people with intellectual disability also have a mental illness (dual diagnosis). These people figure highly in the group who come into contact with the criminal justice system and are often least well assisted by services.

Increasing capacity by changing environmen and support to decrease effects of intellectual disability

A constructive way to look at intellectual disability is to define it in terms of the support needs of people. This approach sees the effect of the disability as something that will vary and can be increased or reduced by external factors. It does not view intellectual disability as an unchangeable characteristic of the individual. The effect of the disability or the capacity of the person is a function not only of the disability but also a function of their environment and the support they receive.

Adjusting the environment and the support to meet the person’s needs can increase the person’s capacity and reduce the effect of the disability.

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How is intellectual disability different to other cognitive disabilities?

Mental illness

  • Often episodic
  • Affects perception and mood- e.g. schizophrenia, depression, bipolar affective disorder (used to be known as manic depression)

For further information contact the Mental Health Information Service

Telephone- 1300 794 991


Acquired Brain Injury

  • can be caused by stroke, accident or drug/alcohol
  • can impair memory, thinking, perception, attention and emotions. The brain injury can result in disinhibited behaviour or poor impulse control
  • People may rehabilitate over time i.e. years

For further information: contact the Brain Injury Association

Freecall - 1800 802 840

Telephone - (02) 9868 5261


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  • loss of short-term memory
  • progresses into confusion/disorientation
  • Alzheimer’s Disease is one type of dementia

For further information about Alzheimer’s disease: contact the Alzheimer’s Association

Telephone- 02 9805 0100



  • affects ability to relate to people and the world around them
  • Impairs particularly social interaction, communication and behaviour (e.g. obsessive and repetitive behaviour)
  • People with autism often experience overwhelming anxiety, frustration and confusion
  • Most people with autism will also have some degree of intellectual disability although those with Asperger’s syndrome (one form of autism) typically have average to above average intelligence

For further information: contact the Autism Association of NSW

Telephone - (02) 8977 8370

Autism Information Line- 1800 069 978


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Communication Tips

It is important to convey simple messages when communicating with people with intellectual disability. The following communication tools will be useful to enhance the effectiveness of the communication with a client with intellectual disability:

  • give permission to say “I don’t get it”. Acknowledge that this is hard stuff. For example, “I need to make sure I explain it properly. Please tell me if I’m not clear enough”. Most people with an intellectual disability will try to bluff their way through rather than ask
  • check that the person understands – but own the checking or the person may think they gave you the wrong answer
  • use short sentences, simple language, no jargon
  • one idea at a time
  • slow down
  • abstract concepts are especially difficult; be concrete, for example: time may be a difficult concept; connect to something meaningful to the person – “before or after dinner”, “what was on television at the time?”
  • expect an answer but be prepared to wait. With some people you may need to wait an uncomfortable time to make sure there has been time for the person to process the information and answer
  • try not to interrupt. Don’t finish the person’s sentences
  • sign post “OK, that’s all I need to know about that. Now can we talk about ….”
  • open questions and encourage free recall – let the person tell their story
  • remember body language messages – these speak very loudly for someone with an intellectual disability
  • minimise distractions
  • breaks are essential – the person is likely to have limited concentration
  • reinforce the important messages

for futher information about intellectual disability, please download and refer to An Introduction to Intellectual Disability

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An Introduction to Intellectual Disability

Topics discussed in this document:

  • What is intellectual disability?
  • Definitions of disability
  • A different view of disability
  • Recognising intellectual disability from other conditions
  • Appropriate language
  • Disability etiquette
  • Communication tips
  • Writing in Easy English
  • Disability standards and discrimination

Please click on the link to download complete document- An Introduction to Intellectual Disability

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