Summary: Between 1998 and 2018, the number of people diagnosed with autism has jumped by 787%. The rate of increase was greater for females, with the greatest rise in adults being diagnosed with ASD.
Source: University of Exeter
The number of people diagnosed with autism has jumped by 787 percent in the past two decades, a new study shows, likely an effect of increasing recognition.
The exponential increase – between 1998 and 2018 – was greater for females than males, with the greatest rises among adults.
Researchers compared the rates of autism recorded in GP records in England, covering over 9 million patients from GP practices.
The study, published in the Journal of Child Psychology and Psychiatry, suggests the diagnosis of Asperger’s disorder, a form of autism that does not have attendant intellectual disability, was increasingly applied until the diagnosis was officially scrapped in 2013.
The research suggests increases could be due to increased reporting and application of diagnosis. This is the first study to analyse the time trend of autism diagnosis in a population-based UK clinical cohort by developmental stage, level of severity and by gender, over a twenty-year period.
Differing rates of increase between subgroups suggest effects are primarily due to increased recognition, although an actual increase in autism incidence cannot be ruled out.
A UK policy introduced in 2009 to invest in adult assessment centres may underpin the rise in adult diagnosis.
“As there is not really a plausible reason why autism should increase more in adults and females our study suggests the change is probably due to increased identification, and not more people with neurodevelopmental disorders per se.” said lead author Ginny Russell, from the University of Exeter.
“However, autism is not like a continent awaiting discovery. The definition of what constitutes autism has changed over time, and females and adults were not often thought of as having autism 20 years ago. The vocal work of charities and media coverage, combined with changes in policy has led to more assessment centers for adults, and an autism narrative that many women and girls identify with. Consequently, demand for diagnosis has never been higher.”
Data was taken from the Clinical Practice Research Datalink (CPRD) primary care database, which contains patients registered with practices contributing data to the CPRD between 1998 and 2018. A total of 65,665 patients had a diagnosis of autism recorded in 2018.
The findings also highlighted increased age of diagnosis over time within each developmental stage. In preschools this could be partly because diagnosis of autism in younger children is obviously complex and may need to go at the family’s pace. De-stigmatization of the label due to work by the neurodiversity movement and parent-led lobby groups may have contributed to rising demand for diagnosis in order to access support, outstripping the capacity to carry out assessments in clinical practice.
Autism is popularly conceptualized as a ‘male’ disorder. In response there has been a drive toward referral of more females. The study, which shows a marked growth in female diagnoses compared with males, suggest such initiatives have been having an effect.
The research was conducted by Ginny Russell, Sal Stapley, Tamsin Newlove-Delgado, Andrew Salmon, Fiona Warren and Anita Pearson from the University of Exeter, Tamsin Ford from the University of Cambridge and Rhianna White from the University of Bath.
Time trends in autism diagnosis over 20 years: a UK population-based cohort study
Autism spectrum disorder is a diagnosis that is increasingly applied; however, previous studies have conflicting findings whether rates of diagnosis rates continue to grow in the UK. This study tested whether the proportion of people receiving a new autism diagnosis has been increasing over a twenty-year period, both overall and by subgroups.
Population-based study utilizing the Clinical Practice Research Datalink (CPRD) primary care database, which contains patients registered with practices contributing data to the CPRD between 1998 and 2018 (N = 6,786,212 in 1998 to N = 9,594,598 in 2018). 65,665 patients had a diagnosis of autism recorded in 2018.
Time trend of new (incident) cases of autism diagnosis was plotted for all, and stratified by gender, diagnostic subtypes, and developmental stage: infancy and preschool, 0–5 years old; childhood, 6–11 years old; adolescence, 12–19 years old; adults, over 19 years old.
There was a 787%, exponential increase in recorded incidence of autism diagnoses between 1998 and 2018; R2 = 0.98, exponentiated coefficient = 1.07, 95% CI [1.06, 1.08], p < .001. The increase in diagnoses was greater for females than males (exponentiated interaction coefficient = 1.02, 95% CI [1.01, 1.03], p < .001) and moderated by age band, with the greatest rises in diagnostic incidence among adults (exponentiated interaction coefficient = 1.06, 95% CI [1.04, 1.07], p < .001).
Increases could be due to growth in prevalence or, more likely, increased reporting and application of diagnosis. Rising diagnosis among adults, females and higher functioning individuals suggest augmented recognition underpins these changes.