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Intellectual disability

Summary

A person with an intellectual disability may have difficulty learning and managing daily living skills. This is due to impaired cognitive (thought-related) processing before the age of 18 years, resulting in an IQ below 70. However, everyone is unique. How a person functions in their daily life depends on many factors, not just their IQ level.

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Intellectual disability affects around two to three per cent of the population of Australia. A person with an intellectual disability may have difficulty learning and managing daily living skills. This is because their cognitive (thought-related) processing is impaired.

Children and young people have different abilities and develop at different rates. Some children find learning new skills or information difficult. This may be because they have an intellectual disability.

Intellectual disability is not a psychiatric or mental health problem. A person is said to have an intellectual disability if before they are 18 years of age they have both of:

  • An IQ (intelligence quotient) below 70 (average IQ is 100)
  • Significant difficulty with daily living skills, including looking after themselves, communicating and taking part in activities with others.

Intellectual disability affects some people more than others. Approximately 143,600 Victorians are affected, or about 2.9 per cent of the population. The majority of people with an intellectual disability are mildly affected (approximately 85 per cent). Not all seek or receive disability services. However, there are many services available to help people achieve and maintain an independent lifestyle.

Characteristics of people with an intellectual disability


Every person is unique, regardless of their IQ score. Everyone has their own personality and areas of ability and areas of difficulty. Generally speaking, a person with an intellectual disability:
  • Learns and processes information more slowly than people without an intellectual disability
  • Has difficulty with abstract concepts, such as money and time
  • Has difficulty understanding the subtleties of interpersonal interactions.

Causes of intellectual disability


There are many causes of intellectual disability. A specific cause can be identified in approximately two thirds of cases. Known causes include:
  • Brain injury or infection before, during or after birth
  • Growth or nutrition problems
  • Faulty chromosomes and genes
  • Babies born long before the expected birth date – also called extreme prematurity
  • Health problems during childhood
  • Drug use during pregnancy, including excessive alcohol intake and smoking
  • Environmental deprivation
  • Exposure to toxins
  • A range of medical disorders.

Prevention of intellectual disability


While most cases of intellectual disability have no known cause, measures that may help prevent some of the known causes include:
  • Prenatal screening
  • Not using alcohol, nicotine or illicit drugs during pregnancy
  • Early detection of ‘high-risk’ pregnancies
  • Using folic acid supplements to prevent neural tube defects
  • Screening tests for newborn babies
  • Early detection of health problems
  • Identifying special educational needs of children
  • Regular visits to maternal and child health services
  • Using child safety equipment to prevent injury – such as bike helmets, car seats and capsules
  • Improving nutrition
  • Universal immunisation, including rubella vaccination for girls and women
  • Avoiding exposure to harmful chemicals
  • Prompt treatment of childhood illness
  • Providing an enriching and stimulating environment for children
  • Genetic counselling.

The needs of people with an intellectual disability


Arbitrary categories of mild, moderate, severe and profound levels of intellectual disability are defined on the basis of IQ scores. These levels give some guide to the level of support someone might need, but the way the person functions in their life also depends on other factors, including:
  • Personality
  • Coping skills
  • Other disabilities – for example, physical, social or sensory
  • The amount of support offered by family, friends and the community
  • What is demanded of them in different situations – for example, at home or at work.

People with a mild intellectual disability


A mild intellectual disability is defined as an IQ between 50 and 70. A person with a mild intellectual disability:
  • Can participate in and contribute to their family and their community
  • Will have important relationships in their life
  • May find the subtleties of interpersonal relationships and social rules difficult to fully understand. They may sometimes behave awkwardly or inappropriately in social situations
  • May marry and raise children with the support of family, friends and support services
  • May have a job, in either open or supported employment
  • May live and travel independently, but may need support and help to handle money, and to plan and organise their daily life
  • May learn to read and write, with appropriate teaching. People who have an intellectual disability are likely to have difficulty with academic learning, and their reading and writing may be at a basic level. Some people may not have had the educational support they needed to learn to read or write, and they may be self-conscious about this. It is important to be sensitive when asking people to read information or complete written forms.

People with a moderate intellectual disability


A moderate intellectual disability is defined as an IQ between 35 and 50. A person with a moderate intellectual disability:
  • Will have important relationships in their life and will probably form valued and lasting friendships
  • Will enjoy a range of activities with their family, friends and acquaintances
  • May be able to learn to travel on regular public transport routes with specific training, but will have difficulty planning trips and handling money. They may have great difficulty problem solving when unexpected events occur
  • May learn to recognise some words in context, such as common signs including ‘Ladies’, ‘Gents’ and ‘Exit’
  • Will be able to make choices and understand daily schedules or future events, if they are provided with visual prompts such as daily timetables and pictures of planned events
  • Will need lifelong support in planning and organising their life and activities
  • May develop independence in personal care, such as toilet hygiene, dressing and bathing. This will depend on opportunities to learn and practise these tasks, and whether or not the person has other disabilities, such as cerebral palsy.

People with a severe or profound intellectual disability


A severe intellectual disability is defined as an IQ between 20 and 35. A profound intellectual disability is defined as an IQ below 20. A person with a severe or profound intellectual disability:
  • Will usually recognise familiar people and may have strong relationships with key people in their life
  • Is likely to have little or no speech, and will rely on gestures, facial expression and body language to communicate needs or feelings. Communication systems for people with this level of disability generally rely on photographs or objects to support understanding. For example, you might use a cup or a photograph of a cup with the spoken question: ‘Would you like a drink?’
  • Will require lifelong help with personal care tasks, communication, and accessing and participating in community facilities, services and activities.

Tips for communicating with a person with an intellectual disability


Tips that may help when talking with someone who has an intellectual disability include:
  • Make sure you have the person’s attention. Use their name, gain eye contact or respectfully touch their arm.
  • Start by assuming a person can understand you, then adjust your level of communication according to their response.
  • Ask the person how they would like to communicate if they do not use speech. This could include using communication aids or devices, answering with a way of saying ‘yes’ or ‘no’ to questions (for example, using eye gaze, or head or hand movements), sign language, gestures or facial expressions. If you are not able to understand the person, you may need to ask whoever is accompanying them to assist you.
  • Use appropriate language for the person and the situation – for example, simple, clear words and short, uncomplicated sentences. If the person is an adult, do not speak as though they are a child.
  • Use visual information such as pictures, diagrams, signs, objects, gestures or miming to improve understanding.
  • Use a respectful tone and volume. If the person does not understand you, try a different way of providing the information or asking the question – don’t assume that raising the volume of your voice will help.
  • Don’t rush. Allow the person the time to listen, process your words and respond. Waiting patiently conveys interest in and respect for what they will say.
  • Check if they have been able to understand what you have said by asking them to rephrase in their own words. Do not simply ask, ‘Do you understand?’ because people will often say ‘yes’ to avoid embarrassment or because it is the answer they think you want to hear.
  • If you think you have not been understood, try repeating your message more slowly or using different words. It is your responsibility to make sure your message is understood accurately.
  • If you don’t understand the other person, do not pretend to understand. Be honest and take responsibility for any communication breakdowns. For example, say: ‘I’m sorry, I don’t understand what you’re telling me. Would you please tell me again?’
  • If you cannot understand or be understood, try another approach. Is there another way you can communicate what you want to say? Ask if it’s okay to involve someone who is familiar to the person (a family member or support worker).

Independent living for people with an intellectual disability


If you have an intellectual disability, it means:
  • You still experience and feel things like joy, anger, pride, hurt, jealousy and other emotions
  • You want the opportunity to have a range of life experiences
  • You learn and develop more slowly than average, but you can learn to adapt to new situations and enjoy life independently.

Expressions such as ‘mentally retarded’ or ‘mentally handicapped’ are misleading and negative. Using terms like these can lead to community ignorance, which further isolates people with intellectual disabilities.

Services for people with an intellectual disability


The many services available through the Victorian Disability Services Program include:
  • Family and individual support
  • Help for adults with daily living needs
  • Support for people living in the community
  • Help with finding a suitable place to live
  • Legal advice
  • Specialist healthcare
  • Specific help for individual people.

Where to get help

  • Your doctor
  • Maternal and Child Health service
  • Your local community health centre
  • Your local council
  • Centre for Developmental Disability Health Victoria Tel. (03) 9902 4467
  • Scope Tel. (03) 9843 3000
  • Yooralla Community Learning and Living Centre Tel. (03) 9916 5800, TTY (03) 9916 5899
  • Disability Intake and Response Service Tel. 1800 783 783, TTY 1800 008 149
  • Your Department of Human Services regional office

Things to remember

  • People with an intellectual disability often learn slowly, but can adapt to new situations and enjoy usual life experiences.
  • Terms like ‘mental retardation’ are inappropriate.
  • There are many resources available in the community to help people with intellectual disabilities to lead independent lives.
  • Categories of mild, moderate, severe and profound levels of intellectual disability are defined on the basis of IQ score. Factors such as personality, presence of other disabilities and social support also play important roles in how the person functions in their daily life.
  • Always show respect for the person and communicate in ways that acknowledge the age of the person and the value of their contribution.

You might also be interested in:

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This page has been produced in consultation with and approved by:

Centre for Developmental Disability Health Victoria

(Logo links to further information)


Centre for Developmental Disability Health Victoria

Fact sheet currently being reviewed.
Last reviewed: March 2012

Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.


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A person with an intellectual disability may have difficulty learning and managing daily living skills. This is due to impaired cognitive (thought-related) processing before the age of 18 years, resulting in an IQ below 70. However, everyone is unique. How a person functions in their daily life depends on many factors, not just their IQ level.



Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your qualified health professional. Content has been prepared for Victorian residence and wider Australian audiences, and was accurate at the time of publication. Readers should note that over time currency and completeness of the information may change. All users are urged to always seek advice from a qualified health care professional for diagnosis and answers to their medical questions.

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