Introduction, definitions and key legislation: Intellectual disability


Caution is needed when defining and describing the capacity of people with an intellectual disability, as their abilities are frequently underestimated. The internationally accepted diagnostic criteria, the forms of cognitive impairment and key legislation is explained.

Defining intellectual disability

“Intellectual disability” is the term used in Australia to describe individuals who have impaired cognitive functioning evidenced in childhood. The same condition is described as “learning disability” in the United Kingdom and, until recently, “mental retardation” in the United States, where it is now called “Intellectual Disability (Intellectual Developmental Disorder)”.

The legal definition of intellectual disability in Victoria is found as item (b) of the definition of “disabilities” in section 3 of the Disability Act 2006 (Vic) (“Disability Act”):

Intellectual disability in relation to a person over the age of five years, means the concurrent existence of:

a significant sub-average general intellectual functioning; and

b significant deficits in adaptive behaviour,

c each of which became manifest before the age of 18 years.

See the definition of “disability” under “Disability Act” in Understanding disability and the law.


Before 1 July 2006, the same definition was contained in the Intellectually Disabled Persons’ Services Act 1986 (Vic) (“IDPSA”) [repealed].

Test and diagnostic criteria

The Disability Act (s 6(3)) sets out the test for determining whether or not a person has an intellectual disability. Sections 4 to 9 set out other important provisions in relation to people who have an intellectual disability.

Current internationally accepted diagnostic criteria for the condition of intellectual disability are more explicit. For example, the recently published fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V), the internationally used manual in relation to diagnosis of mental impairments, states:

Intellectual Disability (Intellectual Developmental Disorder) is a disorder with onset during the developmental period that includes both intellectual and adaptive functioning deficits in conceptual, social, and practical domains.

The following three criteria must be met:

a Deficits in intellectual functions, such as reasoning, problem-solving, planning, abstract thinking, judgment, academic learning and learning from experience, and practical understanding confirmed by both clinical assessment and individualized, standardized intelligence testing.

b Deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, the adaptive deficits limit functioning in one or more activities of daily life, such as communication, social participation, and independent living, and across multiple environments, such as home, school, work, and recreation.

c Onset of intellectual and adaptive deficits during the developmental period.

These DSM-V diagnostic criteria may be useful in arguing before a court that a person has an intellectual disability. However, eligibility for disability services provided or funded by the Victorian Government Department of Health and Human Services (DHHS) is determined by the criteria set out in the Disability Act, or (for the Barwon National Disability Insurance Scheme (NDIS) launch site and other areas of Victoria once they have transitioned to the NDIS) under the National Disability Insurance Scheme Act 2013 (“NDIS Act”). SeeEligibility for services under the Disability Act”.


The National Disability Insurance Scheme (NDIS) was launched in several pilot sites around Australia from 1 July 2013, including, in Victoria, the Barwon Region, and it is intended to be rolled out to the rest of Australia by July 2019. Those in the launch site and, progressively, the rest of Victoria who meet the NDIS eligibility requirements will receive disability services under the NDIS, and no longer under the Disability Act. See Understanding disability and the law, for NDIS Act 2013 definition of “disability requirements”. Intellectual Disability is not treated as a separate category but is included with various disabilities listed in the “disability requirements”.

Caution: generalisations about intellectual disability and capacity

Generalisations about intellectual disability – and about the capacity of a person with an intellectual disability – frequently underestimate a person’s abilities. Intellectual disability may limit a person’s functional skills, ability to learn and understanding of concepts, but there are many degrees of intellectual disability. Many people who have an intellectual disability are able to function very well. Others may need some assistance with some aspects of their life. And others may need significant assistance.

It is vital that each person’s case be assessed individually, and that the views of the person who has an intellectual disability always be sought, taken into account and, wherever possible, acted upon. It should be noted that the aim of the Victorian Government’s State Disability Plan 2013–2016 is for all people with a disability to be fully included in the life of the community, and to have the same opportunities as people who do not have a disability. The Commonwealth Government’s National Disability Plan 2010–2020 contains similar intentions. About 1 per cent of Victoria’s population has an intellectual disability, or approximately 49,000 people.

Intellectual disability and the Disability Act

In the past, there has been general confusion between intellectual disability and mental illness. The Disability Act (and the IDPSA prior to 1 July 2007) and the Mental Health Act 2014 (Vic) make a clear distinction between the two.

Some people may have both an intellectual disability and a mental illness. This is often termed “dual disability” or “dual diagnosis”.

Other forms of cognitive impairment

Until 1 July 2007, when the Disability Act came into effect, no specific legislation dealt with the provision of services to people with other forms of cognitive impairment, such as acquired brain injury (cognitive impairment caused by accidents, organic brain injury or drug use) or some autism spectrum disorders. People who had these or other disabilities may have accessed services funded under the Disability Services Act 1991 (Vic) [repealed] (“DSA (Vic)”) and the Disability Services Act 1986 (Cth) (“DSA (Cth)”). The Disability Act extended this coverage to include people with some other forms of cognitive impairment, such as acquired brain injury.

Autism Spectrum Disorders

Autism, also known as Autism Spectrum Disorders (ASDs), was initially not included in the Disability Act. However, the Victorian Government developed a State Autism Plan, and in 2009 ASDs were acknowledged and included in the Disability Act as a “neurological impairment”. This means that all people with an ASD can now be considered for disability services. (SeeDisability Act” in Understanding disability and the law, for the definition of “disability”, where item 1a of the definition includes the term “neurological”.)

It is estimated that 70 per cent of people who have an ASD also have an intellectual disability. Some of the remaining 30 per cent, although they do not have an intellectual disability, may nonetheless have a disability that requires services to assist them. For example, a child who has Asperger’s Syndrome or high functioning Autism (on the mildest end of the autism spectrum) may require speech therapy, psychological treatment and counselling. Early intervention is extremely important for children with ASDs; the Commonwealth Government provides some funding for this crucial early intervention assistance. Diagnosis of an ASD must be made by a paediatrician before funding can be granted. (See also Understanding disability and the law.)

Key legislation

Two statutes govern the provision of services to people who have an intellectual disability in Victoria, and a third has increasingly done so since 1 July 2013:

the Disability Services Act 1986 (Cth) (“DSA”);

the Disability Act 2006 (Vic); and

the National Disability Insurance Scheme Act 2013 (Cth).

The Disability Act sets out the Victorian Government’s responsibility in relation to people who have an intellectual disability. The Disability Services Branch of the Victorian Department of Health and Human Services (DHHS) is responsible for implementing the aims and objectives of the Act (for contacts see Understanding disability and the law).

The Disability Act contains a list of objectives and principles that apply to all persons covered by the Act (ss 4, 5). The NDIS Act also has a list of objects and principles (s 4).

Section 6 of the Disability Act provides a list of principles and provisions that apply specifically to people who have an intellectual disability, which includes that:

people who have an intellectual disability have a capacity for physical, social, emotional and intellectual development and have the right to opportunities to develop and maintain skills and to participate in activities that enable them to achieve valued roles in the community;

services for people who have an intellectual disability should be designed and provided in a manner that maximises opportunities for people living in residential institutions to live in community based accommodation;

people who have an intellectual disability in a residential institution have the right to a high quality of care and development opportunities while they continue to reside in the institution; and

services for people who have an intellectual disability should be designed and provided in a manner that ensures developmental opportunities exist to enable the realisation of their individual capacities, and that a particular disability service provider cannot exercise control over all or most aspects of the life of a person who has an intellectual disability.

Other relevant legislation includes the Guardianship and Administration Act 1986 (Vic) (see Understanding guardianship); the Crimes Act 1958 (Vic) (ss 50–52) and the Sentencing Act 1991 (Vic).

This chapter focuses on the provisions found in the Disability Act relating to the Victorian Government’s responsibility to people who have an intellectual disability. For general information about the Commonwealth and state disability services Acts, see Understanding disability and the law.

Note that with the advent of the NDIS Act, starting with the Barwon Region launch site, responsibility for planning and provision of disability services will transition from the Victorian to the Commonwealth Government over several years, with full roll-out intended to be completed by 2019. For further details, visit