People with intellectual disability experience deserve parity of care – but currently experience worse health outcomes compared to those without.
Elves have previously blogged about essential aspects of care, including managing aggressive, challenging behaviour in people with intellectual disability (Smith 2024), the wellbeing of parents with children with intellectual disability (Lynch and Tracey 2021), and social care among adults with intellectual disability (Clark 2021). A complex picture emerges when considering delivery of healthcare for people with intellectual disability – including psychiatric support for people with intellectual disability.
In Australia, the 2023 Final Report for the Royal Commission into the Violence, Abuse, Neglect, and Exploitation of People with Disability acknowledged that people with intellectual and developmental disabilities have particular difficulty accessing appropriate services, including mental health services, due to diagnostic overshadowing and systemic neglect and discrimination.
We often talk about diagnostic overshadowing; a clinical bias in which one attributes symptoms to intellectual disability rather than to a psychiatric condition. But how common are psychiatric conditions among people with intellectual disability?
In this record linkage study, Arnold and team (2025) utilised multiple administrative datasets to gather a granular understanding of the prevalence of psychiatric conditions among people with intellectual disability compared to those without in New South Wales (NSW), Australia.
The current study seeks a detailed understanding of the prevalence of psychiatric conditions among people with intellectual disability.
Methods
The authors linked data from 20 individual administrative datasets to identify all the people aged five and over who received disability services in NSW where intellectual disability was recorded as a primary or a secondary disability. They also identified those who have a recorded diagnosis of intellectual disability in health service datasets. The comparison group was obtained from the Medicare Consumer Directory and matched based on 5-year age, sex, and area of residence, with a ratio of 5:1. The study period was set from 1 July 2001 to 30 June 2018.
It is worth noting at this point, that for the purposes of this study, “intellectual disability” is defined as including both developmental disorders (i.e. autism and related conditions, ADHD and learning disorders) and congenital syndromes (Down syndrome being the main congenital syndrome) – which may be different to other jurisdictions.
The presence of psychiatric conditions was collected through hospital admission data collection, emergency department data collection, mental health ambulatory data collection, medicare benefits schedule service data (i.e. private mental health input), and disability-specific datasets. The authors defined serious mental illness to capture those with high service needs by combining diagnostic categories and service use intensity. In this study, the subpopulations of people with inpatient hospital admission for a primary psychiatric diagnosis, those who received care from the ambulatory team with a psychosis-related diagnosis, or those who had hospital admission to a non-emergency department psychiatric unit were classified as having severe mental illness.
To calculate the annualised prevalence, the authors used the number of people who experienced psychiatric conditions in a given financial year as the numerator with the total number of people in the denominator. Further, the study divided intellectual disability into different congenital and developmental conditions.
Results
The study identified 97,644 people with intellectual disability and 451,502 people in the comparison group.
The prevalence of any psychiatric condition among those with intellectual disability was almost double (76.0%) compared to those without (38.3%), and, rates of severe mental illness were more than three times (16.2%) higher than for people without intellectual disability (5.1%). The prevalence was higher for all the psychiatric conditions examined (mood/affective disorder, depression, bipolar disorder, anxiety disorder, substance use disorder, psychotic disorder, self-injury/suicidality, dementia, non-dementia organic psychiatric disorder, personality disorder, developmental disorders, autism, attention-deficit/hyperactivity disorder [ADHD] and learning disorders, and other psychiatric conditions) for those with intellectual disability compared to those without.
Among those with intellectual disability, most people (nearly 95%, n = 41,268) had developmental disorders (i.e. autism and related conditions, ADHD and learning disorders) rather than congenital syndromes (Down syndrome being the main congenital syndrome). Of note, while the rates were higher than the comparison group, people with Down syndrome had lower rates of most psychiatric conditions compared to those with developmental disorders except for dementia (11.4% among those with Down syndrome compared to 2.1 for those with developmental disorders). Among those with developmental disorders, people with ADHD and learning disorders had particularly high rates of psychiatric conditions (89.5%) and severe mental illness (27.2%).
People with intellectual disability are twice as likely to experience any psychiatric condition, and thrice as likely to experience severe mental illness.
Conclusions
The authors concluded that:
we have confirmed the substantially increased prevalence of psychiatric conditions in people with intellectual disability compared to a matched comparator cohort.
Particularly, people with intellectual disability and ADHD experience substantially elevated risk of co-occurring psychiatric conditions.
People with Down syndrome had lower prevalence of co-occurring psychiatric conditions than other people with intellectual disability, except for increased rates of dementia.
People with ADHD and Intellectual disability are at higher risk of co-occurring psychiatric conditions, while people with Down’s syndrome have lower risks, except in respect of Dementia.
Strengths and limitations
Using the multiple existing administrative datasets, the study examined one of the largest cohorts of people with intellectual disability. As the authors point out, however, there are some limitations inherent in using linked administrative data such as:
- People with milder intellectual disability may not access services – for instance, they may not receive education support or disability services. This means that we are likely only examining a subset of the population that may not be generalisable to the extended population.
- Not everyone with psychiatric conditions might access services – so the administrative datasets are unable to capture those with undiagnosed or untreated psychiatric conditions (this is probably most relevant for conditions like self-injury).
- Further, diagnostic overshadowing may be affected by visible disability – People with more ‘obvious’ difficulties, or features of a congenital syndrome like Down’s syndrome, may be more likely to go undiagnosed or misdiagnosed with psychiatric conditions.
In other words, the quality of outcomes is qualified by the quality of information captured in these datasets, which is impacted by systemic biases present when looking at data at an administrative, not granular clinical level. By virtue of design, inherent person-to-person nuances may be lost when evaluating population-level data.
Furthermore, given the significant heterogeneity of care someone with intellectual disability receives in different settings, the findings may not be generalisable to other countries, or even to other jurisdictions within Australia. For instance, access to psychiatrists with expertise in intellectual and developmental disability is greatly variable between regions, with extreme variances in service provision between states.
When analysing large-scale population data, the nuances of individual experience may be lost.
Implications for practice
There were 588,700 people in Australia with an intellectual disability recorded in the 2003 census, which is 3% of the population. Psychiatric care of individuals with an intellectual disability should be a core business for any psychiatrist. At the moment, many of us lack confidence in treating people with intellectual and developmental disability.
Is it too much to ask every psychiatrist, regardless of their interest or training, to be comfortable and competent in assessing and managing common psychiatric conditions among people with intellectual disability?
A 2007 survey of psychiatrists demonstrated that the majority were concerned about supporting unmet care needs for people with disability, but 34% of those surveyed were reluctant to treat adults with intellectual disability (Edwards et al., 2007). This was identified in part due to a lack of curriculum covering the topic in the general psychiatry training program, but one must also wonder about the social influences on these attitudes; particularly a lack of societal inclusion for people with an intellectual or developmental disability. The findings from the current study highlight a couple of important issues for us to consider further, as proactive practitioners.
Having segregated pots of funding for intellectual disability may cast more shadows on the diagnostic complexity. In many countries, disability and mental health services are run by separate departments. For example, in Australia, the National Disability Insurance Scheme is funded by the Department of Social Services, while much of mental health care is funded through the Department of Health and Aged Care. These organisational siloes may make it challenging to integrate healthcare for people with intellectual disability at the structural level, unintentionally building additional barriers to access.
Collectively, there is an imperative for psychiatrists to upskill ourselves, both broadly and specifically. Unlike in the United Kingdom, our College does not have a Faculty of Psychiatry of Intellectual Disability in Australasia. The aforementioned Royal Commission Final report recommended establishing a focused training program for Australasian psychiatrists. While we acknowledge that there are many important and obvious benefits to having a subspecialty field related to intellectual and developmental disability, this should not be the only training focus for our College. If over seven out of ten people with intellectual disability experience psychiatric conditions throughout their lifespan, then this cohort should not automatically be seen as a unique group that requires subspecialist input. Subspeciality input for rare, complex, disability-specific presentations is important – but it should not detract from conceptualising people with intellectual disabilities with whole individual personhoods, when accessing any clinical input.
The views of people with intellectual disabilities are key, and they should be supported to influence their care. Participation in co-design, co-development, and co-production of research and service provision, all help people with intellectual disability to ensure their care needs are accommodated and prioritised, and to improve collegiality between professionals and people with lived experience. It is only by building a large enough professional workforce that can work comfortably with people (with or without intellectual disability), in an evidence-based, autonomy-affirming, and person-centred approach that we can genuinely achieve equitable care for those most underserved by the system.
Seven out of ten people with intellectual disability experience psychiatric conditions throughout their lifespan.
Statement of interests
Shuichi is an associate editor for ANZJP in which the paper was published in.
Melanie was one of the reviewers for the manuscript for ANZJP, and is a member of the curriculum design working group for the RANZCP Section of the Psychiatry of Intellectual and Developmental Disabilities.
Links
Primary paper
Arnold SR, Huang Y, Srasuebkul P, Cvejic RC, Michalski SC, Trollor JN. (2025) Prevalence of psychiatric conditions in people with intellectual disability: A record linkage study in New South Wales, Australia. Australian & New Zealand Journal of Psychiatry. 2025;59(5):433-447. doi:10.1177/00048674251324824
Other references
Clark M. Managing demand for social care among adults with intellectual disabilities. The Social Care Elf, 22 April 2022.
Edwards N, Lennox N, White P. (2007) Queensland psychiatrists’ attitudes and perceptions of adults with intellectual disability. J Intellect Disabil Res. Jan;51(Pt 1):75-81.
Final Report: Royal Commission into Violence, Abuse, Neglect and Exploitation of People with Disability (Australia); last accessed 25 April 2025.
Lynch C and Tracy D. Parents and carers of children with an intellectual disability: what do we know about their wellbeing? The Mental Elf, 1 June 2021.
Smith J. Aggressive challenging behaviour requires personalised interventions, robust caregiver relationships, and sustained system-level support. The Learning Disabilities Elf, 19 August 2024.
