What if I told you that there are a lot more autistics born in the 1980’s than 1 in 10,000. And this isn’t me saying “it’s almost certainly true”. This is fact. I’d hope that one of your first reactions would be, “what should we do with this information to make life better for autistic people?”
Hang around online Autism discussions, especially those involving causation, and you will undoubtedly read someone claiming “back in the 1980’s, the autism rate was 1 in 10,000.” People base this on studies done back in the 1980’s and they assume or assert, “nothing has changed since then”. Which is odd, since a whole lot has changes in autism understanding since the 1980’s.
What if I told you that there are a lot more autistics born in the 1980’s than 1 in 10,000. And this isn’t me saying “it’s almost certainly true”. This is fact. I’d hope that one of your first reactions would be, “what should we do with this information to make life better for autistic people?”
If your first reaction was, “this can’t be true. There’s an autism epidemic because of vaccines or some other pet causation theory”, you have your priorities in the wrong place. If you think you are an autism advocate, you aren’t.
Back to the recent study. When I read a recent study from Denmark, I was amazed. No exaggeration, I was amazed to see data so clearly showing that the Autism Prevalence for autistics born in the 1980’s is much higher than previously reported. I say this with apologies to the study authors, because there’s a lot more in this study. That said, there is also the trend of prevalence* with time. It’s, well, amazing. The study is Cumulative Incidence of Autism Into Adulthood for Birth Cohorts in Denmark, 1980-2012. Basically, the authors mined the Danish Central Person Register for people with autism diagnoses. Here’s the graph from that study (click to enlarge):
There is a phrase for a certain type of graph in my work: spaghetti plots. This isn’t quite that complicated, but it is complicated enough to take some time to walk through. So let’s take that time. Basically, each line shows show data for people born in a given 2 year period as a function of their age. The bottom line, for example, shows data for people born in 1980-81. The data is basically what the autism prevalence would be if someone had reported it in the year for that age.
Let’s take a few examples. Again, for that bottom line (people born in 1980-81). At age 10, the autism prevalence is about 0.02%. So, if you had asked in 1990 (when these autistics were 10), “what’s the autism prevalence for 10 year olds in Denmark”, you’d have been told 0.02%. 2 in 10,000. And if you never looked again, that’s what you’d think the autism prevalence is for people born in 1980. Which is exactly why you hear, “the autism prevalence back in the day was 1 in 10,000.” No one looked again.
But now we have more data. Let’s look at, say, age 20, which would be about year 2000. By this point, the autism prevalence has risen to about 0.13% (about 1 in 800). That’s 6 times larger than when this group was 10. This doesn’t mean that more people “became” autistic. No, it means that people previously undiagnosed were identified. By the time this group was 35 years old (about 2015), the autism prevalence was 0.33% (about one in 300). That’s 16 times larger than when they were 10.
I digitized the data for the 1980-81 group and plotted it. If I get time I’ll make a better graph. It isn’t 100% precise, but here’s that graph (click to enlarge):
Let’s say again what we see here:
1) the autism ‘rate’ for Danes born in 1980-81 is not 1 in 10,000, it’s about 1 in 300. Getting comparable to the autism ‘rates’ reported today.
2) the majority of these autistics were not identified until they were older than 10 years old.
3) the autism ‘rate’ is still climbing today. Yes, they are still diagnosing people well into adulthood.
Now, consider some of the other data in the study. For example, Danes born in 2000-01 had an autism prevalence in 2016 of 2.8%. With no sign of a plateau. When those Danes were 8 years old, their autism prevalence was about 0.77%. Yes, it climbed by a factor of 3+ from age 8 to age 16.
Another way to look at this is: people have been diagnosed throughout the lifespan. And this is still going on.
We’ve only looked at a small subset of the data in this study, but we have to ask ourselves what do we do with these results? I know what I think we need to do:
First, we have to accept that many autistics were not diagnosed when they were children. The autism prevalence in the adult population is much higher than the old data would suggest. It may be (probably is, in my view) close to or the same as the prevalence in children.
Second, we have to accept that the autism prevalence in children is likely higher than what is being reported today. The 2.8% reported for one birth cohort in Denmark is basically the same as that reported in the highest estimates in the U.S.. And there was no sign that this Danish value is the maximum value that will be seen for that cohort, or any other.
Third, and here’s where we need actual action, not just a change in beliefs. If we believe that the supports, services and therapies autistics deserve are different than those targeting other disabilities (which I firmly believe), we should be working harder to diagnose those as yet undiagnosed. This goes for young children as well as adults.
Third, and here’s where we need actual action, not just a change in beliefs. If we believe that the supports, services and therapies autistics deserve are different than those targeting other disabilities (which I firmly believe), we should be working harder to diagnose those as yet undiagnosed. This goes for young children as well as adults.
I am the parent of an autistic teenager. There’s a lot of advice (good and bad) on how to support autistic children. But there’s very little on autism specific supports for adults. And this hasn’t really changed in the past decade or more. One way to get real information is to take a look at what has worked and what has failed for autistic adults. Besides helping those adults and other autistic adults (a good cause in itself), it helps pave the way for the autistic kids coming of age. Well, you know what? It’s hard to do those sorts of studies if we don’t even identify who is and who isn’t autistic in the adult population.
As a final aside, consider the CDC autism prevalence estimates. They use a very different methodology than in this Danish study, which will introduce some differences in the results. That said, the CDC focuses on children 8 years old. The CDC team had good reasons to choose 8 years old, but let’s look at some of the data from this recent Danish study and ask what this tells us about the CDC data. For people born in 2000-2001, the Danish autism prevalence is be about 0.77% at age 8. One might say, “Hey, the CDC autism prevalence for 8 year olds born in year 2000 is 1.13%. Autism is more prevalent in the U.S. than in Denmark.” People making this sort of comparison often then try to fit this into their own favorite causation theory. As in, “Denmark gives fewer vaccines, so vaccines cause autism!”. But, wait. The autism prevalence for Danes born in 2000 is actually 2.8%, well over double the CDC estimate for US kids born in 2000. Makes the comparison of CDC numbers to others a bit of an apples and oranges story.
More to the point, consider graphs of CDC prevalence vs. time. It goes up and up, doesn’t it? Kids born in 2004 have a higher autism prevalence than those born in 2000, right? But if you’ve missed a bunch of the kids because you looked at 8 year olds and many kids aren’t identified by then, can you really say that the number of autistic kids has gone up?
Another way to say this: the CDC data are good for what they are. What they aren’t is an actual census of the fraction of kids who are autistic in any given birth year. Trying to say, “there’s an epidemic” from these data just can’t be done.
But that’s getting off the topic. As I noted above, the real question with these data are not “how do they fit into the failed idea that [exposure x] causes autism”. The real question is, what do we do with the knowledge that there are a lot of autistic adults? That there are a lot of kids, younger and older, who aren’t diagnosed accurately? That autism gets diagnosed through the lifespan? I’ve pointed out what I think above. We act on the data. We do what we should be doing: try to use this information to make life better for all autistics, be they young or old, diagnosed or not.
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By Matt Carey
*note–I am not an epidemiologist. Rather than try to keep bouncing between “incidence”, “cumulative incidence” and “prevalence”, I will use the terms more loosely than an epidemiologist would.
