Autism diagnoses are up, largely fuelled by the NDIS. What happens next isn’t entirely clear

Research published earlier this year found the strongest evidence yet that the introduction of the National Disability Insurance Scheme (NDIS) has played a key role driving up autism diagnoses in Australia.

The study found evidence the increase may be due to clinicians lowering the threshold for an autism diagnosis, rather than a “catch up” in the diagnosis of historically under-diagnosed groups.

But major changes to the NDIS due to start in October this year mean a formal diagnosis will no longer be the main gateway for autistic children to access support. So are autism diagnoses likely to fall?

What’s behind the increase in autism diagnosis?

Autism is a neurodevelopmental condition where people show social and communication differences (for example, in eye contact or speaking), and restricted and repetitive behaviours (for example, a preference for routines or repeated movement).

It is well established that autism is caused by a combination of genetic and environmental factors.

But over the past two decades, the rate of autism diagnosis has increased dramatically worldwide – tripling, by some estimates.

The main reason is that diagnostic boundaries for autism have been redrawn.

Autism was once most often diagnosed in people with significant developmental, intellectual and/or language difficulties. But since the mid-90s, autism has been increasingly understood as a “spectrum”.

This means a person does not need to have intellectual disability or marked language difficulties to receive an autism diagnosis.

A diagnosis can be made if the core features of autism – differences in social and communication behaviours, and restricted and repetitive behaviours or interests – are persistent and meaningfully impact daily life.

As a result, people with a much more diverse range of abilities and support needs have received an autism diagnosis, increasing the overall numbers.

Australia has some of the highest autism rates in the world

The expansion of autism diagnostic boundaries has been observed across the world. But the diagnostic rates in Australia have climbed much faster than in other countries with comparable cultures and economies.

The current rate of autism in Australia is 4.3% for children aged between 5 and 14 years old (up from 3.2% in 2018), compared to 1.8% of 5–19 year olds in the United Kingdom.

One factor unique to Australia – long thought to have contributed to the higher diagnosis rate – was the introduction of the NDIS.

Since its staged rollout across Australia from 2013 to 2020, the NDIS has been the primary pathway through which autistic children can access public funding for therapy and services.

Many anecdotal reports suggest a diagnosis of autism can help children meet eligibility criteria for NDIS support.

Policy makers and clinical and research experts have suggested that higher diagnosis rates in Australia may, in part, reflect clinicians applying a lower diagnostic threshold to enable access to needed supports.

Others have questioned the accuracy of these views, prompting the need for further research to definitively answer this question.

What did the study test?

The recent research examined data from Medicare, the NDIS and Australian Bureau of Statistics. It tested whether the introduction of NDIS was a direct cause of increasing autism diagnosis rates in Australia.

The study took advantage of the gradual rollout of the NDIS across Australia to create a “natural experiment”. In the early part of the rollout, some regions had access to the NDIS while others did not. This allowed the researchers to isolate the effect of the NDIS from broader trends on rising autism diagnosis rates.

Their analysis found geographic regions where the NDIS was introduced had an autism diagnostic rate about 0.56 percentage points higher than areas without the NDIS.

The researchers used statistical modelling to estimate what the growth rate of autism diagnosis would likely have been without the NDIS. They found the NDIS has led to a 32% increase in overall autism prevalence in Australia.

One possible explanation is that this finding reflected a “catch up” in groups that have been historically underdiagnosed, such as girls, older children, and individuals from regional or disadvantaged backgrounds.

However, there was little evidence of this. Instead, increases were larger among boys, children in metropolitan areas, and those from non-culturally diverse backgrounds. There was also no change in the age at diagnosis over time.

The researchers concluded that the NDIS has been a direct cause of the increases in autism diagnosis, most likely because clinicians lowered the diagnostic threshold once the NDIS was introduced.

But the NDIS is undergoing significant reform

In August last year, the federal, state and territory governments agreed to establish a new national disability support program, Thriving Kids.

Thriving Kids is for children aged 0–8 years with developmental delay and/or autism with low to moderate support needs. Children with higher support needs, and eligible adults, are expected to keep accessing support through the NDIS.

Under Thriving Kids, children will be able to access support based on the presence of developmental delays, without a formal diagnosis of autism. So diagnosis will no longer be the gateway to services. This means it is highly possible we will also see the rates of autism diagnoses begin to fall, once Thriving Kids is fully implemented by January 1 2028.

A further practical step would be to strengthen consistency in diagnostic practice, including mandating that clinicians use Australia’s national guideline for autism assessment and diagnosis of autism. Currently, this is not mandatory.

But some experts argue autism now exists as a cultural phenomenon alongside its clinical definition, and believe the motivation for autism diagnoses – among individuals and clinicians – will remain high, regardless of policy changes.

Rigorous epidemiological studies that track autism diagnostic rates across the years of Thriving Kids implementation, and beyond, will be key to answering this question.