Prevalence, Prevalence, Prevalence, Prevalence!

If you have an anti-vaccine agenda, and you want to scare people off vaccines by telling them that vaccines cause autism, and you want to scare them about autism, then all you have to do is get the definition of prevalence wrong. Then, take a national emergency like Hurricane Sandy and write some half-assed blog post about how autism is some sort of a national emergency that needs to be addressed immediately but is being hidden from the public by special interests.

How something that is emergent like that can be hidden remains a mystery to me, but — as always — facts don’t ever get in the way of a good anti-vaccine, anti-government, big conspiracy nut’s blog post. Like this one here. If you can stomach it, go read it, then come back for today’s breakdown of the [redacted] spewed there.

Let us begin with two quick definitions. “Incidence” is the number of new cases of a disease or condition divided by the number of people at risk. For example, the incidence of cervical cancer would be the number of new cases divided by the number of women with cervices. Note that we don’t include men in that rate/proportion because men don’t have uteri nor cervices.

“Prevalence” is the number of existing cases of a disease or condition divided by the total population. For example, the prevalence of diabetes is the number of total diabetes cases in a community divided by all of the people in that community. These two numbers, incidence and prevalence, tell you very different things epidemiologically. Only incidence can tell you if you have an outbreak, or national emergency, on your hands.

For a condition such as autism, where the person who has autism rarely, if ever, dies from it and can lead long, productive lives, the prevalence rate will continue to climb and climb as more people are diagnosed and more of them are living long. Even if the incidence (new cases) drops precipitously, the fact that there are new cases will mean that prevalence will continue to rise. I’ve explained this to you before, haven’t I?

I have.

I really wish the author of that post had an epidemiologist who she could ask about these things before looking foolish. All she has is an even more hardcore anti-vaxxer who is trying to become an epidemiologist. But that’s a whole other story.

Anyway, back to the post in question. In it, the author states the following:

“Starting in the 1980s the autism rate began an ever-ascending climb. 

1995 1:500
2001 1:250
2004 1:166
2007 1:150
2009 1:110
2012 1:88″

She quickly acknowledges having been told the reason for this climb in prevalence, but she immediately refutes it:

“For years the medical community has been credited with “better diagnosing” of a disability that’s always been around. In other words, we’ve always had people like this in society– we just didn’t call it autism… The trouble is, no one has ever had to prove the claim of “no real increasing—better diagnosing.””

Allow me to highlight the troubling part of her statement:

“…no one has ever had to prove the claim of “no real increasing —  better diagnosing”

No one? Really? What about this, this, this (.pdf), and this? Those don’t count because of [insert conspiracy theory here]? Oh, well, I tried.

And then she gets all conspiracist about it:

“That hasn’t stopped authorities from claiming that they’re out there somewhere, undiagnosed or misdiagnosed. It would be especially interesting to see the 40, 60, and 80 year olds with classic autism, whose symptoms are evident to all. It would be of real significance to find middle aged and elderly people whose health history also included normal development until about age two when they suddenly and inexplicably lost learned skills and regressed into autism.”

In other words, because the author doesn’t see them, they must not exist.

Tell me something. Do you “see” people with schizophrenia everywhere? Well, you should. You should see them because 1.1% of the world’s population suffers from it. As it turns out, 1.1% is 1 in 88.

Let that settle in for a little bit. Maybe get up and stretch and whatnot.

Based on prevalence, there are just as many people with schizophrenia as there are people with autism. In the cases of both conditions, the prevalence will continue to increase not because there is some “tidal wave”, “hurricane”, or “emergency” of number of incident cases. Nope. The prevalence will continue to increase because people with these conditions are being treated and accepted — diagnosed and intervened on — and allowed to be part of society. No longer are they being institutionalized in the same manner or proportion as they were in the past.

But we don’t “see” them everywhere because these kinds of conditions manifest themselves at A) a certain age, and B) as a spectrum. You don’t see kids with schizophrenia because it manifests in young adulthood. You don’t see a lot of schizophrenic adults because they are either being treated for their condition and lead “normal” lives or are institutionalized (e.g. sanatoria or even jail). Likewise, you don’t “see” autistic children everywhere because, well, seriously, how many of us wander around elementary schools? And the 1 in 88 adults? I’ll get to that in a second.

By the way, I have several friends with mental health issues, including schizophrenia, and central nervous systems that are not typical, and I love them to death. But I digress…

The author of the misinformed, misconstrued blog post then want to see the following:

“The problem is no one has ever been able to show us the one in 88 adults with autism.”

The author wants to believe — or make her readers believe —  that 1 in 88 adults has autism. I hope it’s an oversight on the author’s part because the prevalence rate on autism is for children. Here, I’ll show you:

“About 1 in 88 children has been identified with an autism spectrum disorder (ASD) according to estimates from CDC’s Autism and Developmental Disabilities Monitoring (ADDM) Network.”

It’s children. There are less children than adults in the United States. So you can’t extrapolate that number willy-nilly without use of some biostatistics. Again, if only she had a [expletive] epidemiologist to help her sort these things out and not read so idiotic.

Finally, if you can do me a favor and not even mention the author’s name in the comments. She’s been known to go all “decepticon” and have her bot fill comments sections with what can be best described as manure.

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6 thoughts on “Prevalence, Prevalence, Prevalence, Prevalence!

  1. Funny, I volunteered for organisations with autistic adults who where (then) diagnosed with mental retardation, emotionally disturbed or learning disabled* in the late 1980s to early 1990's. More than half of those adults were already in their 50's and living in group homes and not seen by the general public. *The regular staffers would often complain how the clients were misdiagnosed even then.

  2. Just found this blog! As an infectious disease epidemiologist, this a huge find. Keep up the good work and I'll spread the word about the blog to my colleagues. Cheers.Mike

  3. "You don't see a lot of schizophrenic adults because they are either being treated for their condition and lead "normal" lives or are institutionalized (e.g. sanatoria or even jail). Likewise, you don't "see" autistic children everywhere because, well, seriously, how many of us wander around elementary schools?"This, a thousand times.I have burned deeply into my mind an interview I watched a long time ago: an actress reporting having a disabled sibling and how both of them meet an old-fashioned crone who scorned her "when one has childs like this, one hides them!"

  4. I promise not to mention her name Reuben…we all know who the "bot" is. This is just another in a long line of whining complaining articles that she and the other *journalists* at that blog write. We are *treated* to such articles on every holiday, as well as every day of remembrance that we observe as Americans. This, however, has to be a new low for that gang. The *bot* sitting in her comfortable home in the midwest, has no compassion for the personal losses experienced by people in the path of hurricane Sandy. Sixteen bodies were found in homes in Staten Island, New York…the total death count is 80 and expected to climb.As usual, your explanation of the "tsunami" of ASD diagnoses is spot on. Too bad that the stalker/student doesn't understand epidemiology; he may graduate with a MPH degree, but he will never be an epidemiologist.Hmmm, that same old false argument that she and her readership have never seen older people with autism/autistic-like behaviors…ergo there are no older people, who lived in institutions, that were human warehouses, before humane alternatives in group homes were developed for them.http://www.youtube.com/watch?v=k_sYn8DnlH4(I never *toured* Willowbrook State School, but I have been in the back wards of Developmental Centers, State Schools and State Mental Hospitals).

  5. I think of heard of that author. Yeah, facts don't particularly matter to that person."You don't see a lot of schizophrenic adults because they are either being treated for their condition and lead "normal" lives or are institutionalized (e.g. sanatoria or even jail)."And some you don't "see" because, sadly, they are homeless, the ignored.

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