Yes, there are a lot more adult autistics than commonly thought. The real question is what we do with this information.

13 Mar

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.


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.

6 Responses to “Yes, there are a lot more adult autistics than commonly thought. The real question is what we do with this information.”

  1. Broken Link March 13, 2019 at 23:39 #

    Thank you for this, Matt. There are some pretty clear inflection points on that graph. It would be really interesting to try this for some other cohorts and see if the inflection points line up with the changes to the DSM.

    • Sullivan (Matt Carey) March 14, 2019 at 00:11 #

      Here’s the table from the paper (there’s one table, on figure. It’s only 2 pages).

      There’s what appears to be a pretty significant jump in the numbers going from the change from ICD-8 to ICD-10. 1994. For the 1980-81 cohort, that’s the jump at age 14. And it looks like there’s a jump for the other cohorts as well in 1994.

      • giftbearer March 26, 2019 at 22:11 #

        I don’t see how scientists can even measure this accurately when the definition and criterion for Autism is constantly changing as well as how symptoms/traits are interpreted differently by one professional versus another.

        Also, given that for many years people commonly believed it “went away” as a person reached adulthood, many adults’ symptoms/traits were misdiagnosed as other conditions, and still are.

        Then on top of that, many professionals that know how to recognize it in males still don’t understand how it can present differently in females, so therefore a whole bunch of females are routinely overlooked even today with more written about this in the literature.

        In addition, there are people who actually work in the field who don’t get the concept of why services for adults are needed. To those of us who found out later in life it is like living all our lives in a foreign country where we don’t speak the language. I tried unsuccessfully to explain this to a woman I met who runs a support group for people with Asperger’s. Apparently that didn’t mean she understood it one iota. Her day job was working with people who were so severely affected that they couldn’t function on any level, so in her eyes anyone who functioned better than that was just fine and didn’t need any help. She was oblivious to the fact that those of us who never received appropriate services are out here flying by the seat of our pants moment by moment and really have no place to turn when we have questions about how we are supposed to navigate this world. If we were to tell most people we encounter in the course of our lives everything we don’t know they either wouldn’t believe us (because of our masking) or would assume we were stupid (because they assume every adult on earth knows these things if one is reasonably intelligent). Adults on the spectrum are really caught between a rock and a hard place.

        The public/community needs to start listening to adults on the spectrum and what we need, but first they need to trust us that we in fact do have needs to be met and that we do struggle on a day-to-day basis. At this point in time acknowledging that there are many people falling through the cracks, and coming up with some empirical creative solutions to that systems problem is probably more crucial than developing statistics on incidence.

  2. doritmi March 14, 2019 at 17:42 #

    Thank you, this is a very important article.

  3. Scientistabe March 14, 2019 at 18:18 #

    Reblogged this on The Blood-Brain Barrier Scientist.

Trackbacks/Pingbacks

  1. Anti vaccine activists are angry about a new study…and they didn’t even bother to read it | Left Brain Right Brain - March 14, 2019

    […] just wrote about the autism prevalence study: Yes, there are a lot more adult autistics than commonly thought. The real question is what we do wit…. I have the graph from the prevalence study, so I ran the numbers quickly. If we limit ourselves to […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: