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The number of diagnosed cases of autism has increased substantially in the last decades as seen in the following graph.

enter image description here

Bar chart of the number (per 1,000 U.S. resident children aged 6–17) of children aged 6–17 who were served under the Individuals with Disabilities Education Act (IDEA) with a diagnosis of autism, from 1996 through 2007. Image from Wikimedia Commons

How can this increase be explained. Are there environmental factors that contribute to a higher rate of autism today? Or did we just get better at diagnosing autism?

Mad Scientist
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    You talk about decades, but the graph just shows one decade + a year. – user unknown Feb 28 '11 at 01:52
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    Who says we're getting better? An increased number of diagnosed cases could also mean we're getting worse at diagnosis and that there are many more "false positives". Especially with something that gets as much press and money as autism, there are many incentives for a false positive. – Russell Steen Feb 28 '11 at 19:14
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    *Pedantry alert* I don't care how much the rate is going up... *it's **not** an "epidemic" unless there is an **infectious** vector!* Grrr.... – dmckee --- ex-moderator kitten Oct 02 '11 at 15:11
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    @dmckee The meaning of 'epidemic' has long since transcended just infectious diseases. – Fomite Oct 04 '11 at 21:34
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    @dmckee: If only it were infectious, we could develop a vaccine for it. And wouldn't *that* be a dilemma for the anti-vaccination crowd! – Bruce Alderman Dec 13 '11 at 16:00
  • @BruceAlderman their claims would be true then an autism vaccine would cause autism...sort of. – Ryathal Dec 14 '12 at 20:06
  • "who were served under the Individuals with Disabilities Education Act" -- How does this relate to the frequency of the disorder??? – Daniel R Hicks Nov 14 '18 at 01:21
  • I'm closevoting this because it's not quoting any claim that there's an epidemic. – Andrew Grimm Nov 14 '18 at 02:15
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    @BruceAlderman [Relevant SMBC](https://www.smbc-comics.com/comic/autism-and-vaccines) – Punintended Nov 14 '18 at 17:47

2 Answers2

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First of all if you look at the original data, things are way more suspicious. Why are they suspicious? Because most mental illnesses are actually also increasing dramatically during that period.

One can speak about epidemiology of a single disease, but when there are many diseases with the same trend, producing that graph is clearly cherry-picking the data to show that there must be something wrong with autism in particular!

So this leads us clearly to systematic causes, like improved diagnostics, changed diagnostic criteria and age at which the diagnosis can be produced, etcetera.

Obviously this doesn't disprove that autism has increased. It might have increased as well, but it's hard to say in a situation in which a proper study hasn't been conducted.

Let me quote Wikipedia:

  • More children may have autism; that is, the true frequency of autism may have increased.
  • There may be more complete pickup of autism (case finding), as a result of increased awareness and funding. For example, attempts to sue vaccine companies may have increased case-reporting.
  • The diagnosis may be applied more broadly than before, as a result of the changing definition of the disorder, particularly changes in DSM-III-R and DSM-IV.
  • Successively earlier diagnosis in each succeeding cohort of children, including recognition in nursery (preschool), may have affected apparent prevalence but not incidence.
  • A review of the "rising autism" figures compared to other disabilities in schools shows a corresponding drop in findings of mental retardation.

The article also contains a pretty damning conclusion:

The reported increase is largely attributable to changes in diagnostic practices, referral patterns, availability of services, age at diagnosis, and public awareness.

The following studies are referenced (emphasis mine):

More children are being diagnosed with ASDs today than in the past. Some of the prevalence increase is undoubtedly attributable to changing diagnostic tendency; however, there are insufficient data to determine whether this can explain the entire increasing trend.

—source

The prevalence of autism in metropolitan Atlanta in 1996 for children aged 3 to 10 was 3.4 per 1000. This overall rate is 10 times higher than rates from 3 other US studies that used DSM-III or ICD-9 criteria to identify children with autism and pervasive developmental disorders in the 1980s and early 1990s. Our rate is closer to that found in a recent prevalence study in Brick Township, New Jersey, that used DSM-IV criteria (4.0 per 1000 for autistic disorder and 6.7 per 1000 for the entire autism spectrum). Our findings also are similar to rates from several recent European studies that used ICD-10 or DSM-IV criteria (2-6 per 1000 for autism).

—source

Glorfindel
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Sklivvz
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  • +1, pretty damn to the point. DSM-IV was published in 94, though. Surely, the new definitions would've caused a massive increase, but is it reasonable that it should explain any of the changes we're seeing in the time span the chart covers? – David Hedlund Feb 26 '11 at 11:25
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    The article credits three studies for "pretty damning conclusion." Rather than quote Wikipedia on this, you should take a look at those studies. – Borror0 Feb 26 '11 at 13:58
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    Wikipedia isn't really a great source to be used to reach a conclusion. If Wikipedia cites a source for its statement, we should use that source. If it doesn't it's just some random guy's opinion. – DJClayworth Mar 04 '11 at 21:59
  • Isn't a good point also that population is increasing? – Chris Dennett May 12 '11 at 01:14
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    @Chris the figures quoted in the original question are diagnoses per 1,000 US residents. – John Lyon May 12 '11 at 02:17
  • Ahhh, gotcha :) – Chris Dennett May 12 '11 at 02:24
  • Also: the diagnostic criteria was widened in the early 90s. – horatio May 12 '11 at 14:21
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    @Borror0 added studies – Sklivvz Oct 02 '11 at 08:39
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    Do you have better source than the "original data" link to back up "most mental illnesses are actually also increasing dramatically during that period."? That only shows a dramatic increase in Developmental delay (644%), autism (377%), and "other health impairments" (185%). "Mental retardation" actually shows an 18% drop - although if they were all essentially moved to autism that alone could explain over half the increase. – joshuahedlund Sep 16 '13 at 14:36
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    This situation isn't dissimilar to the "Breast Cancer Epidemic" in South Brazil - after several prevention campaigns, cancer numbers went up by a lot, and people started to blame the mammograms and the touch exams for it. Obviously, the more you check for a disease the more cases go unnoticed, which can create this weird effect of "exams causing cancer/other disease". – T. Sar Nov 14 '18 at 11:14
  • @T.Sar "the more you check for a disease the more cases go unnoticed"? – pipe Nov 15 '18 at 12:30
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    @pipe Explained myself badly. The idea is that the more you check for the diseases, more you find them. English isn't my first language, and sometimes stuff that works on my primary language with a meaning turn out WAY different in english. – T. Sar Nov 16 '18 at 09:48
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A South Korean study, that was recently covered by Steven Novella at the Neurologica blog found that - if you actually look carefully - the incidence of autism is around 2.6% (i.e. 26 on your chart), which is much higher than the normal diagnosis rate, and around double what was than previously thought.

This has a number of consequences, including:

  • providing support for the idea that we will continue find many more cases as we look harder (even without the underlying rate of incidence changing), and
  • also supporting the idea that there is a spectrum of symptoms and severity for autism. This makes the prevalence very dependent on our definitions of when autism is considered a disorder.

These ideas are discussed further by Steven Novella, in the above article.

Sébastien
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Oddthinking
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    When I was a kid in the 50s, there was no "Autism". There were only varying degrees and types of mental retardation. We even carefully classified such children as "idiots" or "cretins" or "morons" depending on their perceived IQ or equivalent development by age. I don't think I encountered the word "autism" till the 70s. We had a friend in "special education" at the time, and there was a brief period where autism became a sort of fad diagnosis as it sounded better than simply being "retarded". – M. Werner May 12 '11 at 23:34
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    Just so we are clear: Mental Retardation (http://en.wikipedia.org/wiki/Mental_retardation) is a different diagnosis to Autism (http://en.wikipedia.org/wiki/Autism) or being somewhere on the Autism Spectrum (http://en.wikipedia.org/wiki/Autism_spectrum). That autism was rarely diagnosed in the 1950s (after being coined in 1910) but is commonly diagnosed now is the question being looked at. If symptoms that were formerly classed as mental retardation are now classified as autism, that would explain the data, but we need more than an anecdote to support it. – Oddthinking May 13 '11 at 09:33
  • That was precisely what the guest on NPR's Talk Of The Nation said in a recent program; that they were now more carefully able to diagnose the Autism spectrum of syndromes, whereas previously they just tended to get lumped in with the general "retardation" diagnosis. – M. Werner May 13 '11 at 16:01
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    not just "more carefully", but more profitably. With drugs, therapy sessions, etc. all generating more income for autism now, there's more incentive for practitioners to diagnose it than simply "mental retardation" for which there is afaik no treatment. Same reason the "diagnoses" of ADHD among teens have exploded at around the same time. – jwenting Oct 03 '11 at 09:16
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    Both A and B, in my opinion. We're seeing more autism because we're LOOKING for it more. It's also a topic which is well funded - and you have to have funding to do research. I think it's also terribly short-sighted of people to focus on one 'cause' of a problem and not try to think 'outside the shot'. If *I* had the funding, I'd like to examine the rates/histories/occurrences of pharmaceuticals and POP's in our waters/soils. – Darwy Apr 01 '12 at 08:35
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    @Oddthinking: I think the point he's trying to make is that psychological assessment of children in the 1950s was little more than a raging disaster of overgeneralization, oversimplification, and misdiagnosis combined with an attitude of tossing these kids into mental institutions as part of some kind of twisted eugenics program. Things *are* quite a lot better for autistic children these days. The treatment available for my brother was vastly inferior to the treatment currently available to my son. – Ernie May 17 '17 at 17:15
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    @jwenting Turned on it's head (with respect to the morals behind), given there are treatments, it may also be more likely to help someone with autism than general retardation, therefore a pragmatic approach would be to preliminary try treatment to either confirm the diagnosis or rule it out. That's what House would do anyway^^ – Frank Hopkins Nov 16 '18 at 18:35
  • @Darkwing there is no treatment for autism, the most we can hope for is therapy (either things like CBT and/or medication) to suppress or otherwise deal with the worst of the symptoms. And that same treatment would also be applicable to suppress those same symptoms in people without autism, especially depressives and people with general anxiety disorder (which are both very common among autistic people). – jwenting Nov 19 '18 at 04:59
  • @jwenting wouldn't that invalidate your point about it being more lucrative to treat for autism? – Frank Hopkins Nov 19 '18 at 09:49
  • @Darkwing it's highly lucrative to prescribe people pills they need to take for the rest of their lives rather than something that makes the problem go away permanently. – jwenting Nov 19 '18 at 09:55
  • @jwenting that would be an argument to develop symptom pills rather than permanent treatments (which only works as long as no one else finds a permanent treatment), but it wouldn't be an argument to diagnose autism over something else, if - as you said - the same pills can be prescribed for people that are not diagnosed with autism, but the broader general retardation, simply based on the symptoms those pills treat. – Frank Hopkins Nov 19 '18 at 10:00
  • @Darkwing the previous diagnosis ("mental retardation") has no treatment for the symptoms at all, for autism there's a range of symptom suppressing treatments on the market already at no additional cost. Which diagnosis would you prefer based purely on economics? Mind, autism is no cakewalk for those who suffer from it. But I've a feeling the diagnosis is being applied too often, just like that of ADHD. – jwenting Nov 19 '18 at 10:05
  • @jwenting In that case my original statement stands, I'd rather first give the treatment for autism symptoms a try and if they don't work have an additional indication that autism isn't what I have , rather than directly end up with another (untreatable) diagnosis. So my point is, while money could be a (morally dirty) motivator for some players, in particular pharmaceutics producers, a pragmatic treatment approach can be a (morally clean) motivator for some players (primarily doctors) as well. – Frank Hopkins Nov 19 '18 at 10:25
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    @jwenting "there is no treatment for autism, the most we can hope for is therapy": I think you meant to say that there is no *cure* for autism. Therapy *is* treatment. – phoog Nov 24 '18 at 05:13
  • @phoog there is no treatment. The most one can hope for is learning people to live with it and suppress some of the secondary symptoms (like the ever prevalent anxiety attacks). I have had psychotherapy for those myself, as well as walking around with a nitroglycerin spray for over a year. – jwenting May 07 '19 at 07:51
  • @jwenting my point is that nitroglycerin sprays and psychotherapy *are* treatments. A treatment that is effective only for the suppression of symptoms is still a treatment. – phoog May 07 '19 at 13:02
  • @phoog my point is that they're treating secondary conditions that often occur side by side with the autism, not the autism itself. There is no treatment for my inability to detect non-verbal communication effectively for example, nor for my seriously reduced ability to express emotions, both symptoms of autism itself rather than the sister conditions of social and general anxiety disorder that go along with it. – jwenting May 08 '19 at 03:38
  • @jwenting I see. That makes more sense. Thank you for clarifying. – phoog May 08 '19 at 04:57