Abstract
Background
Autism/Takiwātanga is a lifelong neurodevelopmental condition that is currently estimated to impact 2.3% of children. It is characterised by persistent social and communication differences, sensory issues, and restricted repetitive patterns of behaviour or interests. While associated with strengths such as visual thinking, logic, and memory, the effects of autism on adaptive functioning can result in a need for a range of supports in order for autistic people to live their daily lives. Common co-occurring conditions include intellectual disability, mental health conditions such as anxiety, depression, and attention-deficit/hyperactivity disorder (ADHD), and physical health conditions such as asthma, epilepsy, and gastrointestinal problems.
Autistic young people are at risk of health, academic, social, and behavioural difficulties that can result in long-term deleterious effects on social inclusion, employment, adaptive functioning, and overall quality of life. In particular, they are more likely to experience inequities in health, education, and the criminal justice system (CJS).
There is lack of quantitative data on autism in Aotearoa/New Zealand and an absence of population-level lifecourse research. Notably, there is no registry for autism, and no recognised method for identifying cohorts of autistic people using administrative data. Therefore, autism research in Aotearoa/New Zealand is typically restricted to small clinical samples or is based on survey information.
The Integrated Data Infrastructure (IDI) is a large research database, curated by Statistics New Zealand, and contains a wide range of data about people and households from national administrative collections and surveys. The breadth of data in the IDI represents one of its key strengths as it links data across multiple life domains, including, but not limited to, health, education, and the CJS. Moreover, these are population-level data, making the IDI a world-leading source of information for research. Use of the IDI presents a unique opportunity for research in Aotearoa/New Zealand, one that has yet to be explored with respect to autism and which has the potential to make important contributions to international literature. Effective use of existing administrative data offers opportunities to better understand autism and meet Aotearoa/New Zealand’s obligations under the United Nations Convention on the Rights of Persons with Disabilities including collecting disability data and conducting research in domains such as health, education, and the CJS.
Aims
The overall aim of this thesis is to understand the impacts of autism across the lifecourse using linked administrative data contained within the IDI. There are four specific aims:
1) Explore ways in which the IDI can be used to identify autism among children and young people aged 0–24 years, describe differences in subsequent rates of autism by sociodemographic characteristics, and examine rates of co-occurring mental health and related conditions in this group.
2) Examine medication dispensing for autistic children and young people and compare dispensing and polypharmacy rates among those with autism, ADHD, and the general population.
3) Quantify differences in suspension rates from school for autistic compared to non-autistic students and assess whether high need education-based funding is associated with differential suspension rates for autistic students.
4) Explore CJS interactions, including with police, courts, and corrections for young autistic adults compared to non-autistic people and assess whether offence types differ.
Methods
The studies in this thesis are quantitative and used linked population-level health and non-health administrative data from the IDI. Participant populations were established using IDI-based methods for establishing Aotearoa/New Zealand estimated resident populations or, in the case of the birth cohort study design (Chapter 6), using birth registration data.
Autistic cases were identified using an IDI-based case identification method developed as part of this thesis (Chapter 3). This method uses diagnostic information captured within three health data sets; publicly funded hospital admissions, publicly funded secondary specialist mental health service use, and disability support services needs assessment information. An individual was indicated as autistic if they had an autism diagnosis in one or more of these data sets.
The primary outcomes explored included autism and co-occurring mental health and related conditions (Chapter 3), medication dispensing and polypharmacy (Chapter 4), stand-downs and suspensions (Chapter 5), and interactions with police, courts, and prisons (Chapter 6).
Sociodemographic information was captured in the IDI personal details table. This includes sex, age, and ethnicity determined using the major ethnic groups defined by the New Zealand Standard Classification: European, Māori, Pasifika, Asian, Middle Eastern/Latin American/ African (MELAA) and Other. Socioeconomic status, using the New Zealand Deprivation Index, and urban/rural profile of residence were derived using historical residential address information from the IDI address notification table.
This study was reviewed by the University of Otago Human Research Ethics Committee as a ‘Minimal Risk Health Research – Audit and Audit related studies’ proposal and received ethical approval (Reference: HD17/004). Access to the IDI and approval for the study was provided by Statistics New Zealand.
Results
The autism case identification method yielded a cohort of 9,555 children and young people (0.57% of the Aotearoa/New Zealand estimated resident population of 0-24 year olds). Among eight-year-olds (the rate that aligns with CDC annual autism prevalence estimates) the corresponding rate was 0.98% (or 1:102). Rates of autism were highest among males (0.88%), those aged 5-9 (0.90%) and 10-14 years (0.86%), and Europeans (0.68%), and lowest amongst Māori (0.49%), Pasifika (0.39%), and Asians (0.45%), as well as those living in high deprivation (0.53%) and rural areas (0.46%). Autistic young people were found to have high rates of co-occurring mental health and related conditions with 68% affected by at least one condition, including intellectual disability (30%), emotional conditions (anxiety and/or depression) (28%), and ADHD (27%).
Analysis of medication dispensing revealed that autistic young people faced a high medication burden. In a one-year period, autistic young people were dispensed four unique medications on average, including relatively high rates of psychotropic, asthma, and gastrointestinal medications. They also experienced high rates of polypharmacy with 57% experiencing polypharmacy of three or more medications (36% higher than non-autistic people), and 11% experiencing extreme polypharmacy of 10 of more medications (over twice that of non-autistic people).
Rates of school suspension were found to be nearly three times higher among autistic students compared to non-autistic students (adjusted odds ratio 2.81; 95% confidence interval [CI] 2.55-3.11). However, high need education-based funding support in the form of the Ongoing Resourcing Scheme (ORS) was associated with significantly reduced suspension rates among autistic students (adjusted odds ratio 0.29; 95% CI 0.21-0.40). This meant that autistic students with ORS funding experienced suspension at approximately the same rate as their non-autistic peers.
Analysis of CJS data revealed that young autistic adults were significantly less likely than their non-autistic peers to be proceeded against by police (adjusted hazard ratio 0.62; 95% CI 0.56-0.70), charged in court (adjusted hazard ratio 0.61; 95% CI 0.53-0.70), and convicted in court (adjusted hazard ratio 0.57; 95% CI 0.48-0.67). However, there was no significant difference in the risk of being imprisoned (adjusted hazard ratio 1.01; 95% CI 0.67-0.1.51). Moreover, among those charged with a crime, autistic people were at greater risk of being charged with serious offences deemed punishable by two or more years in prison (adjusted hazard ratio 1.73; 95% CI 1.44-2.14).
Conclusions
This collection of studies demonstrates the value of employing linked population-level administrative data to conduct lifecourse research into the experiences of autistic children and young people as they interact with health, education, and criminal justice systems. The findings describe challenges and inequities experienced by autistic people in Aotearoa/New Zealand including disproportionately high rates of co-occurring physical and mental health problems, higher risk of suspension from school, and evidence of differential treatment within the criminal justice system. The study also highlights the value of effective support policies and advocacy in improving these outcomes. It changes the landscape of autism research in Aotearoa/New Zealand by demonstrating ways in which the IDI can be utilised to improve understanding of autistic people and their experiences. It also identifies further opportunities for cost-effective research such as examination of labour market outcomes for autistic people and research to understand the experiences of parents and siblings of autistic children.