Analyzing the 2012 CDC Numbers on Autism Rates
Since the United States Centers for Disease Control released its latest statistics on autism prevalence last week, I have done a series of images, blog posts, and videos analyzing the new data. This post collects all of those things in one place for people who want an extensive analysis of what the new report means.
Although I have grown somewhat more concerned about the proposed changes in autism diagnosis for DSM-5, I think the variation from state to state and within different ethnic groups in the report proves that the current state of autism diagnosis is intolerably random and bad.
The other disturbing thing to me about both the report and the way it is being discussed is the fact that everyone seems to be ignoring the evidence from Britain that indicates that the rate of autism among children and adults is consistently about 1% of the population. There is a great deal of speculation regarding why the rate has changed so dramatically, and it seems to me that it should at least be informed by this information:
The only study to look for autistic adults in a national population was conducted in Britain and published in 2009. Investigators interviewed 7,461 adults selected as a representative sample of the country and conducted 618 intensive evaluations.
The conclusion: 1% of people living in British households had some form of autism, roughly the same rate that the U.S. Centers for Disease Control and Prevention estimates for children in America today.
The British study found it didn't matter whether the adults were in their 20s or their 80s. The rate of autism was the same for both groups.
Some speculation of my own:
I do not think the number of autistic people has changed very much, but I do think that more people are visibly disabled by their autism than has been the case in the past. Many people are investigating environmental causes such as various toxins and chemicals. I wish there would be more investigation into changes in the information environment as well.
Video version of the above post.
One out of every 54 boys in the United States has an autism spectrum disorder.
One out of every 252 girls in the United States has an autism spectrum disorder.
The big surprise for me in the new autism statistics that just came out from the United States Centers for Disease control is that the discrepancy between boys and girls has actually increased. Now, boys are 4.6 times more likely than girls to have an identified autism spectrum disorder, instead of four times. And then I remembered that these numbers are actually from 2008. I think that awareness that there are autistic women who are not named Temple Grandin has increased tremendously in the last four years, and I think that we will probably see a change in the other direction with the next set of data.
Why are do there appear to be so many more autistic boys than there are autistic girls?
The one factor that definitely plays a role is sexism. You see some hint at this in the CDC report itself:
In all seven sites reporting data on intellectual ability, a higher proportion of females with ASDs had intellectual disability compared with males, although the proportions differed significantly (52% for females and 35% for males; p<0.01) in only one site (North Carolina). When data from these seven sites were combined, 150 (46%) of 328 females with ASDs had IQ scores or examiners' statements indicating intellectual disability compared with 608 (37%) of 1,653 males.
In other words, girls are less likely to be diagnosed with autism unless they also have intellectual disability.
Girls are less likely to be diagnosed with autism, even when they display the same degree of severity:
Ginny Russell explained: "Boys were more likely to suffer from severe autistic traits, whether diagnosed with an ASD or not. However, even with the severity of autistic traits held constant, boys were still significantly more likely to receive an ASD diagnosis than girls.
"Boys are more than four times more likely to have ASD and are clearly more likely to suffer from these types of symptoms. More interesting is our finding that even with symptom severity held constant, there is still a gender bias towards diagnosing boys. Our analysis suggests that girls are less likely to be identified with ASD even when their symptoms are equally severe." The researchers suggested that the popular conception of autism as a 'male' disorder may contribute to this bias.
I tend to believe that the popularity of Simon Baron-Cohen's theory that autism represents an "extreme male brain" probably has something with the movement toward even more bias in favor of boys in diagnosis than was previously the case. In England, where his work is about twice as influential as it is the United States, researchers found men were nine times more likely to be autistic than women.
Also, testing seems to be biased to be favor of showing the kind of autistic traits boys are more likely to have, according to research done by Somer Bishop, Marisela Huerta, and Catherine Lord:
In focus groups, Huerta says, parents of girls often note that the questions don’t capture what is unusual or abnormal about their daughters’ play habits.
Unlike the stereotype of the boys with autism, girls with the disorder are often interested in imaginative play — obsessively so, in some cases. “You don’t expect to see a kid with autism being obsessed with a baby doll,” says Bishop.
Similarly, a girl with the disorder may be socially interested and motivated, but unsuccessful in forming relationships with her peers. “We get referrals from families who are frustrated because they know in their gut that something is not going well in terms of their child’s overall development, but can’t quite figure out why things are so hard for their girls,” Huerta says.
There do seem to be significant differences in the way that autism tends to manifest itself in men and women, although it's always to important not to take generalizations based on gender too seriously.
But these differences do mean that is very important to have both male and female autistic representation.
I decided to focus on the good part about the new appointments to Interagency Autism Coordinating Committee, which is that there are three autistic members, and they are all brilliant and compassionate guys. But they are all male, and that's a problem.
It's also a problem when autism projects include only autistic women and no autistic men, which they too often do. These new numbers underscore for me the need to do more to involve more autistic men in our discussions, in our organizations and in our planning.
In the video, I get into these sensitive issue in some more detail, and am probably somewhat more controversial.
Video version of the above post.
Video version of this post at the end.
Here is what the new Centers for Disease Control report says about autism and intellectual ability:
Data on intellectual ability are reported for the seven sites having information available for at least 70% of children who met the ASD case definition (Figure 2). When data from these seven sites were combined, 38% of children with ASDs were classified in the range of intellectual disability (i.e., IQ ≤70 or an examiner's statement of intellectual disability), 24% in the borderline range (IQ 71–85), and 38% had IQ scores >85 or an examiner's statement of average or above-average intellectual ability. The proportion of children classified in the range of intellectual disability ranged from 13% in Utah to 54% in South Carolina. The two sites with the highest proportions of children classified above the range of intellectual disability (IQ >70) were Utah (87%) and New Jersey (73%). In all seven sites reporting data on intellectual ability, a higher proportion of females with ASDs had intellectual disability compared with males, although the proportions differed significantly (52% for females and 35% for males; p<0.01) in only one site (North Carolina). When data from these seven sites were combined, 150 (46%) of 328 females with ASDs had IQ scores or examiners' statements indicating intellectual disability compared with 608 (37%) of 1,653 males.
This is how I interpret this:
1) IQ is an antiquated concept. The idea that a person has a fixed amount of "intelligence" that will remain the same for his or her entire life does not match well with what we know now about the brain and learning. Teenagers' IQs can change as much as 20 points in a few years:
Professor Cathy Price and colleagues administered IQ tests and MRI scans to 33 healthy teens -- the first time in 2004, when the kids were 12 to 16 years old, and then a second time in 2007-08, when they were age 15 to 20. They found changes in individual subjects' performance on the tests, with verbal IQ, nonverbal IQ and composite IQ fluctuating up or down, in some cases around 20 points. In all, 39% of the sample had a change in verbal IQ, 21% in nonverbal IQ and 33% in composite IQ.
2) IQ tests are especially unreliable for autistic people. An IQ test is a snapshot, showing the subject's performance on one day, on one task. The capacity of autistic people to succeed on these tests varies more, in most cases, than the capacity of a neurotypical person from day to day and from one set of circumstances to another. This makes a somewhat unreliable process extremely scattershot in its effectiveness.
3) IQ tests may not match the communicative capacity of an autistic person. If you cannot communicate your ideas to another person, there is no way to test how intelligent they are. Rose Eveleth emphasizes the importance of using nonverbal IQ tests with autistic children, after explaining some of the differences between verbal and nonverbal intelligence tests:
The average child will score around the same percentile for all these tests, both verbal and nonverbal. But an autistic child will not. Isabelle Soulieres, a researcher at Harvard University, gave a group of autistics both WISC and the Raven test to measure the difference between the two groups. Although she expected a difference, she was surprised at just how big the gap was. On average, autistic students performed 30 percentile points better on the Raven test than on WISC. Some kids jumped 70 percentile points. "Depending on which test you use, you get a very different picture of the potential of the kids," she says. Other studies have confirmed this gap, although they found a smaller jump between tests.
4) We can assume that the scores in the CDC report are probably artificially low because of these difficulties.
5) There are still a significant number of autistic people who do have intellectual disabilities.
6) Autistic people with intellectual disabilities matter just as much as anyone else. They are people, and they are part of our community. I care very much about keeping them safe, creating opportunities for them, gaining from their contributions, and making them welcome.
Video version of the above post.
Autism, Race, and Ethnicity
From the report, on autism, race, and ethnicity:
Estimated ASD prevalence also varied by race and ethnicity (Table 2). When data from all sites were combined, the estimated prevalence among non-Hispanic white children (12.0 per 1,000) was significantly greater than that among non-Hispanic black children (10.2 per 1,000) and Hispanic children (7.9 per 1,000). Estimated ASD prevalence was significantly lower among Hispanic children than among non-Hispanic white children in nine sites and significantly lower than among non-Hispanic black children in five sites. Only one site (Florida) identified a significantly higher ASD prevalence among Hispanic children compared with either non-Hispanic white or non-Hispanic black children. New Jersey was the only site that identified approximately the same estimated ASD prevalence among non-Hispanic white children, non-Hispanic black children, and Hispanic children. Estimates for Asian/Pacific Islander children ranged from 2.2 to 19.0 per 1,000 although wide confidence intervals suggest that these findings should be interpreted with caution.
The only thing I have to say about autism and race is that it is clear that we are doing a better job of diagnosing Caucasian children. This embarrasses and angers me. We do not live in a post-racial society.