Bonus episode: The Autism Curve

Episode Summary

Executive Summary: This episode of The Autism Curve examines the dramatic rise in autism diagnoses and argues that the trend is driven at least partly by changing definitions and major underdiagnosis, especially in older adults. Using UK and US data, the program shows huge increases in recorded diagnoses while highlighting that many autistic people, particularly the elderly, were likely missed for decades.

Main Topics: Defining autism and its diagnostic criteria (Priority: 5/5): Ginny Russell explains autism as defined in the DSM: persistent social-communication difficulties plus restricted/repetitive behaviors and sensory differences, with severity varying across a spectrum. The rise in autism diagnoses over time (Priority: 5/5): The episode presents large increases in diagnosis in the UK and US, emphasizing that the growth is steep enough to be described as exponential and demands explanation. Underdiagnosis in older adults (Priority: 5/5): Joshua Stott’s research suggests diagnosis rates are dramatically lower in older people than younger groups, indicating many autistic adults, especially elders, were never identified. How prevalence assumptions affect interpretation (Priority: 4/5): The discussion shows that estimates of how many people are autistic depend heavily on baseline prevalence assumptions, such as 1% versus 3%, which shape conclusions about undercounting. Overdiagnosis versus missed diagnosis (Priority: 4/5): The episode weighs whether rising numbers reflect overdiagnosis in children or underdiagnosis elsewhere, with Stott arguing underdiagnosis is the main issue. Autism as a changing social and medical category (Priority: 4/5): The framing suggests that autism is not just a fixed condition but a concept whose meaning, visibility, and diagnostic boundaries have shifted over time.

Key Arguments: Autism is defined clinically by social-communication difficulties plus restricted/repetitive behaviors and sensory differences, but expression is highly heterogeneous across the spectrum. The increase in autism diagnoses is substantial: UK GP data showed an approximately 800% rise from 1998 to 2018. Similar upward trends appear across Europe and in the US, where CDC figures rose from 1 in 150 children to 1 in 36. Stott’s age-stratified research suggests diagnosis rates in teenagers were about 150 times higher than in the elderly, which is unlikely to reflect real prevalence and implies major underdiagnosis later in life. The number of undiagnosed autistic people in the UK in 2018 was estimated at between 440,000 and 1.2 million, depending on prevalence assumptions. The episode argues that miscounting may explain much of the autism curve: the rise is not necessarily only more autism, but also improved recognition plus long-standing invisibility in some groups. Overdiagnosis may exist in some contexts, but the program frames underdiagnosis—especially among older adults—as the more compelling explanation from the data discussed.

Data Points: Increase in autism diagnoses in England (1998-2018): about 800% - UK GP-record study using data from roughly nine million patients Study sample size: about 9 million patients - England GP surgery records analyzed over 20 years Autism diagnosis increase in the US: from 1 in 150 to 1 in 36 children - CDC data comparing 2000 with the present in the transcript US percentage change: about 300-400% increase - Derived from CDC autism prevalence figures over 20 years Diagnosis rate by age: about 150 times higher in teenagers than in the elderly - Joshua Stott’s age-stratified findings Estimated undiagnosed autistic people in the UK (2018): 440,000 to 1.2 million - Range depends on whether 1% or 3% prevalence baseline is used Lower-bound prevalence assumption: 1% - Based on an active case-finding study discussed in the episode Upper-bound prevalence assumption: 3% - Used as a higher estimate for expected autism prevalence Male-to-female ratio in earlier prevalence study: 9:1 - Cited as one reason the 1% estimate may underestimate true prevalence Published prevalence finding in active case-finding study: about 1% - Terry Brugha study referenced as a baseline estimate CDC prevalence ratio in the US: 1 in 36 - Current reported figure for children with autism in the transcript

Pivotal Quotes: "something curious is happening. There has been an increase of 270% in the number of children presenting with autism." — Michael Blastland: Opening framing of the episode’s central question about rising diagnosis rates "overall there was about an 800% increase in autism diagnosis between those years" — Ginny Russell: Describing findings from a 20-year England GP-record study "I would absolutely agree that that isn't plausible of the true prevalence in the population." — Joshua Stott: Responding to the huge age gap in diagnosis rates and implying major underdiagnosis in older adults

Implications: The episode suggests that rising autism numbers should not be read simply as an epidemic, but as evidence of shifting definitions and major historical undercounting. For services and families, this means better identification—especially in adults and elders—may be as important as debates about overdiagnosis.