You’ve probably already heard—the CDC’s estimate of the autism rate was announced as 1% today. This was published in an MMWR came out today, with the new CDC prevalence estimate of 1 in 110. I made some notes on the conference call, but I thought it worthwhile to make a few comments on the document itself.
In each they estimate the prevalence for 8 year olds. So, the 2000 study was on children born in 1992 and the 2002 study was on children born in 1994. They found prevalences of 1 in 166 (200) and 1 in 150 (2002), respectively.
The new prevalence is 1 in 110 for 2006 (8 year old children born in 1998). This is a big jump, no doubt. It is worth taking very seriously. Unfortunately, it isn’t as simple as saying, “the number of autistic children has increased”.
As the authors note in the introduction:
Since the early 1990s, the number of persons receiving services for ASDs has increased substantially. However, identifying children for services for autism might not be equivalent to using consistent diagnostic standards to identify persons in the population because services within communities are not available uniformly to all persons with ASDs. For this reason, studies that rely exclusively on single-source administrative datasets (e.g., disability service records or annual reports of special education counts) most likely underestimate ASD prevalence and might not adequately capture changes in the ASD population over time
Most of the states reporting in the ADDM use more than a single source. Most use medical and educational records. Those that use a single source (e.g. Florida) show lower prevalence estimates.
Let’s get back to that 1% estimate. This is a big jump in the prevalence—with the previous prevalence being 1 in 150 (about 0.67%). Yes, it should be taken seriously, but at the same time 1% is not a surprising number. The authors list 5 studies that show a prevalence >1%, using other methods.
Note that this is for the 1998 birth cohort, children born 4 years after those studied in the previous MMWR. I bring this up because the “buzz” before the MMWR was discussing this as the 1996 cohort. The studies are not spaced out evenly in time—2000, 2002, 2006.
The methodology is through a record screen, not through direct observation of children:
Children aged 8 years with a notation of an ASD or descriptions consistent with an ASD were identified through screening and abstraction of existing health and education records containing professional assessments of the child’s developmental progress at health-care or education facilities.
If on review of the records, the child is deemed to meet the DSM-IV criteria for autism, he/she is counted. This is a good way to get an estimate, but there is a lot of room for children to fall through the cracks, in my opinion. As such, it is and has always been, an underestimate. In some cases, it is probably a very large underestimate. As will be shown below, there is a big variation by state—a factor of 3. I don’t think anyone really believes that the autism prevalence in Florida, or the prevalence amongst Hispanics is much lower than in other states or other ethnicities.
It is interesting to note that the ADDM network does find a significant number of children whom they (the ADDM) categorize as autistic even though they haven’t been given that diagnosis before. About 23% of the autisistics counted in the 1% value were not identified before the ADDM did their review.
That’s worth repeating—about 23% of 8 year olds identified as autistic were mislabeled as non-autistic by their schools, parents and doctors. That’s an interesting fact for those who claim that autism is easily identified.
The CDC study is not capable of explaining whether part of the increase represents a “real” increase in the number of autistic kids. It certainly can’t go into whether or not any specific proposed cause is valid. However, one can use the data to test hypotheses. This type of study just isn’t capable of making claims about causation.
States Reporting to the ADDM
This new study covers children born in 1994 living in 11 states:
Alabama, Arizona, Colorado, Florida, Georgia, Maryland, Missouri, North Carolina, Pennsylvania, South Carolina, and Wisconsin.
Note that this is different from the last MMWR, which looked at kids born 2 years earlier (1996) and included sites in:
Alabama, Arizona, Arkansas, Colorado, Georgia, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah, West Virginia , and Wisconsin.
The new study added Florida, but took out Arkansas, New Jersey, Utah and West Virginia. These changes do make it more difficult to compare the prevalence data. They do not explain the increase. By that I mean, it isn’t as though the low prevalence states were removed from the previous MMWR study and high prevalence states were added.
I would have been very interested what happened to the prevalence in New Jersey. The last two MMWRs had New Jersey at about 1%. A good comparison would be if that state had the same autism prevalence or a higher value.
Prevalence by state
Data in Table 2 from the MMWR. Data from 11 states were reported. The prevalence ranged from 4.2 (Florida) to 12.1 per 1,000 (Missouri and Arizona). That’s a big spread, a factor of 3. The highest prevalence was for males in Missouri—19.1 per 1,000 (1.9%, or 1 in 52).
There was some variation in the male:female ratio, from 3.2 (Alabama) to 7.6 (Florida). Again, this shows that there is a big variation by state in how autistics are identified.
Variation by ethnicity.
There is a large difference in the prevalence by ethnicity. This also varies by state. For example, there is a 9.4 White-to-Hispanic ratio in Alabama, but the same ratio is only 0.7 in Florida. In general, Whites are identified more often than either Hispanic or African Americans.
We have a lot of work to do in making sure minorities are correctly identified and getting appropriate services and supports.
Earlier age of identification.
The median age of autism diagnosis is about 4.5 years. This is a big jump down from the 2002 data, which had a median of 5 years. That is a good thing.
This is worth a couple of comments. First, there is still room for improvement. Most of the children had development concerns noted in their records before age 2. The obvious question is whether these children could have been identified sooner. This was one comment stressed by the CDC in the conference call.
It is also worth noting that autism isn’t “obvious” or “easy” to identify autistics. 4.5 years old is the median age.
It is also worth noting that the big jump down in median age of identification is a very clear indicator that, yes, people are getting better at identifying and diagnosing autistics.
The range of age of identification is as low as 2 months (!) to as high as 106 months. The low end is pretty remarkable. I don’t think there are any tests qualified for such young children. At the high end, that is nearly 9 years old. Again, this goes to the idea that autism is not obvious.
One complaint that is always used in these discussions is “what, are you saying that no one noticed these kids?”. No. They likely had other diagnoses or that some concerns were noted about development for them.
Number of kids receiving special education services.
In Colorado, 76% of autistic students are in special education, while in Arizona it is 96%. Is there really such a big difference in the needs of these kids from state to state?
Colorado has only 34% of the autistic students under the primary category of autism. Compare that to Maryland with 76%. Again, it is pretty clear that there is a lot of variation in how special education services are granted by state.
From the MMWR:
Data on cognitive functioning are reported for sites having IQ test scores available on at least 70% of children who met the ASD case definition. The proportion of children with ASDs who had test scores indicating cognitive impairment (IQ ?70) ranged from 29.3% in Colorado to 51.2% in South Carolina (average: 41%)
I find this information rather interesting. Most of the children with IQ data were not cognitively impaired.
2004 Prevalence data.
There was also a small appendix released today, with information on 2004 prevalence data (note that the study noted above is for 2006). Those data show a prevalence of 8 in 1,000, or 1 in 125. This is a “smaller scale effort”
It is interesting to put the data from the various studies into a timeline:
If you recall, David Kirby claimed the new CDC data would support his hypothesis that the Hepatitis B vaccine caused an upsurge. Mr. Kirby mistakenly assumed that the 1% figure would be for the 1996 birth cohort. Mr Kirby then correlated the jump from 1 in 150 to 1 in 100 with the uptake of HepB vaccination in that birth cohort. He stated (incorrectly, we now know):
But according to the CDC’s National Immunization Survey (which also includes parental telephone interviews), only 8% of infant children received the Hep B vaccine in 1992, when that birth cohort showed an ASD rate of 67-per-10,000.
By 1994, the number of children receiving Hep B vaccine had reached just 27%—and the cohort showed a similar ASD rate.
But the Hep B coverage rate had risen to 82% by 1996, when that cohort’s ASD rate rose to around 100-per-10,000.
So, there was a smaller jump that correlates with the uptake in HepB in the 1994 cohort—the rate increased from 0.66% (1994) to 0.80% (1996). Then, two years later, there is a similar jump, from 0.80% (1996) to 0.90%. But, this time without the big increase in HepB vaccination.
Not so dramatic a story with the real data. Just a constant rise.
I hope this highlights some of the information in the study. I wish I had the time to spend to make this summary a bit easier of a read. But, there are other posts to write. Like one talking about Autism Speaks and the way they are capitalizing on the new prevalence numbers with a very deceptive graph.