Sunday, August 22, 2010

PLoS ONE: Children from Wealthier Families More Likely to Meet Criteria for an ASD

EXECUTIVE SUMMARY: A recent study shows that wealthier families are somewhat likelier than middle- and low-income families to have autistic children. The study compares surveillance data on a cohort of eight-year-old children in fourteen areas of the U.S. in 2002 and 2004 whom the CDC decided, based on school and medical records, met diagnostic criteria for ASDs with U.S. Census data from 2000 on eight-year-old children living in those same areas of the U.S. Statistical analyses were done on both groups' demographic data, which showed that the autistic children tended to come from somewhat better-off neighborhoods than the general population of eight-year-old children. Because of the study's use of public-school records, and its inclusion of a sizable group of never-before-diagnosed autistic children, its authors believe the association they found between higher socioeconomic status and higher rates of autism prevalence is not solely due to richer people's unfettered access to diagnostic services, but instead might also reflect some other factor that positively correlates with both autism and higher SES: the authors suggest both advanced parental age and excessive hygiene as potential candidates for this mystery factor.

This article in the Kansas City Star alerted me to a study published in PLoS ONE on July 12, giving the first indications I've seen that the conventional wisdom about autism and social class --- that autism is mainly a disorder of the upper classes --- might have more to it than just the simple fact that people with unfettered access to health care are a lot more likely than people without such access to get diagnosed with autism-spectrum conditions.

The way I had understood it, there was no big mystery there: people who can afford to see a doctor in non-emergency situations are going to get all sorts of things diagnosed at a higher rate than people who can't afford that kind of preventive care. In that framework, a higher rate of autism diagnoses among children from wealthy families says nothing about autism per se; it just serves as one more example of the huge inequality of access to health care here in the U.S.

The study I mentioned --- carried out by Dr. Maureen S. Durkin and her colleagues --- tries to address how much of the association between autism and higher socioeconomic status (which Durkin says shows up about half the time in the existing literature on the topic) is due to this gap in access to health care and how much may be due to other factors yet to be uncovered.

To try to include autistic children lacking formal diagnoses in their analysis, Durkin et al. relied on the CDC's Autism and Developmental Disabilities Monitoring Network, whose methodology is described here* on the CDC's website:
In 2000, CDC established the Autism and Developmental Disabilities Monitoring (ADDM) Network to track the prevalence and characteristics of ASDs in the United States. The ADDM Network is a multiple-source, active, population-based surveillance system that reviews developmental records at educational and health sources and employs a standardized case algorithm to identify ASD cases.
There is also a flowchart showing where they get their data from and how they decide which children are actually autistic; unfortunately, the flowchart is still pretty vague about which "educational and health sources" they use. It does mention that they use "multiple" of each, though.

So, in the years 2002 and 2004, the ADDM Network collected data on 407,578 (in 2002) and 172,335 (in 2004) eight-year-old children living in fourteen areas around the country: the northern half of Alabama; the central region of North Carolina; the Coastal and PeeDee regions of South Carolina; the entire states of Arkansas and West Virginia; parts of the cities of Denver, Colorado; Atlanta, Georgia; St. Louis, Missouri; and Salt Lake City, Utah; and the cities and surrounding areas of Phoenix, Arizona; Baltimore, Maryland; Newark, New Jersey; Philadelphia, Pennsylvania; and Milwaukee, Wisconsin**. Of these children, 2,685 met diagnostic criteria for an ASD in 2002; in 2004, the number was 1,376.

Durkin et al. took the data on all the children determined to be autistic --- minus the ones living in Utah and West Virginia, since those sites didn't provide enough information to determine socioeconomic status for the children living there --- and compared prevalence rates for ASDs across three socioeconomic "tertiles": high, middle and low socioeconomic status, as determined by three factors: 1) percentage of people in the area living above the poverty line, 2) percentage of adults 25 and over in the area who have at least a bachelor's degree, and 3) median household income for the area. They also compared those factors between the autistic children and the general population of eight-year-olds living in the same areas at the time of the 2000 census.

Compared with the general population of eight-year-olds living in the same areas, autistic eight-year-olds are somewhat less likely to live in "poverty areas," or areas defined in the 2000 census as having 20% or more of its families with children living on poverty-level incomes, with 16.8% of autistic children living in such areas and 25.8% of all children living in them.

Similar small-but-noticeable differences show up with respect to the other two factors, median household income and proportion of adults with college degrees. Among the general population, the median household income was $42,898; among families with autistic children, it was $50,114. Autistic children, on average, tended to live in census blocks where a larger proportion of adults 25 and older had bachelor's degrees; 30.3% had them compared with the general-population figure of 24.8%.

These differences kept showing up, even when the comparisons were set up differently: besides comparing autistic children with their (approximate) peers on measures of socioeconomic status, the researchers also compared autism prevalence rates across the three socioeconomic-status categories they'd created, and found that the richest group had the highest proportion of children meeting criteria for autism, the middle-income group had the second-highest, and the poorest group had the lowest. This pattern showed itself across all the racial categories included in the study, too.

Now, the question is, does the design of this study correct sufficiently for (well-established) class differences in access to specialized medical and educational services? Can its findings of autism prevalence increasing with socioeconomic status be taken at face value?

Part of the reasoning behind the authors' contention that at least part of the association between autism and wealth is real lies in their use of school-based, as well as clinic-based, documentation. Theoretically, all children in the U.S. going to public schools are going to be monitored by their teachers and screened for learning and developmental disabilities if they start to have problems with classwork, behavior or social interaction. But not all schools have the resources to make this sort of individualized attention a reality. It probably won't surprise you to hear that schools in districts where poor people live have less money than schools in districts where richer people live, and accordingly the poorer school districts are less likely to employ psychologists, paraprofessionals or even college-educated teachers. With less space and less staff, also, even very dedicated, insightful and observant teachers aren't able to give individual attention to every student they see struggling.

The U.S. educational system might be more equitable than its health-care system --- last I heard, public schools were still legally required to educate every student living in their districts --- but similar issues of accessibility plague both systems. Even if our educational system is technically socialized --- available for free to everyone, paid for with taxes --- there are still huge differences between the kind of education (including special education) you can get at a well-funded school in a primarily upper- or middle-class district and the kind of education you can get at a school in a poor district. The richer districts can levy additional taxes to give more money to their schools, and students going to those schools also pay student fees to cover equipment and activities.

All of this leads me to suspect that ascertainment bias can be just as big a factor in an educational setting as in a medical setting.

The study authors tackle this issue in their Discussion section:

An important limitation of this study was that the ADDM Network surveillance system relies on information for children who have access to diagnostic services for developmental disabilities. We could not rule out the possibility that the quantity and quality of evaluations and the information available for case ascertainment might have varied by SES. We looked for evidence of this by examining the number of evaluations per child with ASD recorded in the ADDM Network surveillance system, reasoning that if the higher prevalence of ASD among children of higher SES was due to increased access to diagnostic services, high SES might be associated with a higher number of diagnostic evaluations per child. However, we found no association between the number of evaluations per child and SES. We also examined the mean ages at diagnosis by SES and found that children of high SES received an ASD diagnosis at an average age of 58.0 months, 1.1 month earlier than those of middle SES (p = 0.2838) and 2.7 months earlier than those of low SES (p <>

The other important factor that somewhat mitigates the effect of differential access to the educational and medical professionals who can diagnose autism and provide autism-related services on this study's outcome is the inclusion of a subgroup within the group of autistic children they studied who had no prior diagnosis of autism; there were enough of these children (1,244) to do a separate statistical analysis of this group to determine whether the association between autism and socioeconomic status still holds up among children who had never been evaluated. The association did still stand: even among those children with no previous diagnoses of ASDs, the ratio of autism prevalence as determined by the CDC of low- to middle- to high-SES children was 0.78:1:1.09. (That is, the poorest children were somewhat less likely to be autistic than the middle-income children, who in turn were somewhat less likely to be autistic than the wealthiest children). It's worth pointing out that the ratio for children with previous ASD diagnoses is stronger in both directions, at 0.70:1:1.25.

While I'm not sure this study goes far enough to correct for huge systemic inequities in availability of services, those two findings --- that number of evaluations per child does not vary with SES, and that autism prevalence does vary with SES among never-diagnosed children --- introduces some doubt in my mind where there had been none before. Maybe there *is* more to this socioeconomic-status thing than just access to diagnostic services. I remain skeptical, but no longer absolutely convinced that ascertainment bias explains everything.

*A more complete description exists in this 2007 article in Pediatric and Perinatal Epidemiology, for which I cannot find the full text anywhere online for free.

**The list of fourteen areas applies to 2002; in 2004, only eight of those areas participated --- Alabama, Arizona, Georgia, Maryland, Missouri, North Carolina, South Carolina and Wisconsin. That's why the numbers are so much lower for 2004.

Durkin, M., Maenner, M., Meaney, F., Levy, S., DiGuiseppi, C., Nicholas, J., Kirby, R., Pinto-Martin, J., & Schieve, L. (2010). Socioeconomic Inequality in the Prevalence of Autism Spectrum Disorder: Evidence from a U.S. Cross-Sectional Study PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011551


Anemone said...

This is really interesting. Personally, I don't have a problem with an actual link between SES and autism prevalence, though of course it would never justify skimping on services for lower SES groups.

If people are worried about differential educational funding for different SES regions, the study could be replicated in other countries where education (and health) are funded differently, to see if that makes any difference.

Jess said...

There is no doubt that I would have been diagnosed as a child if it weren't for my family's socioeconomic status of poverty. So you can see why this type of claim sounds like BS to me.

Lindsay said...

Anemone, there have also been studies like this (i.e., comparing the relative SES of autistic and non-autistic children) done in countries where there is socialized medicine; those studies tend to find no link between SES and autism prevalence.

The authors of the study I wrote about even cite a few: Steffenburg and Gillberg (1986), who collected demographic data on children under 10 years old in two areas in Sweden; Gillberg and Schaumann (1982), who compared SES data on a group of 20 autistic children in Goteborg, Sweden, with that on a control group of 59 randomly chosen seven-year-old children from Goteborg; and Larsson et al. (2005), who collected all sorts of data (i.e., information about gestation and birth, parents' psychiatric histories, and family SES) on a whole generation of Danish children.

All of those studies found no difference in SES distribution between autistic children and the general population of children.

stevethehydra said...

While i still think it likely that at least a large part of the difference in diagnostic rates between class/income strata is due to issues of access to diagnosis, i do have a tentative theory as to why autism may be more prevalent in higher economic classes: reproductive selection.

Assuming that autism is largely genetic in etiology (as seems almost certain given how it "runs in families", although i wouldn't oppose the idea that at least some cases occur from perinatal brain injury, exposure to toxins in the womb, or other similar environmental factors), i would submit that, even if the prevalence of autistic genes *started out* equal across all class strata, autistic people born into wealthy families are significantly more likely to have children than autistic people born into poor families, for reasons:

1) Those born into wealthy families are going to get far better parental and (probably) medical, psychological and educational support than those born into poor families, which makes a massive difference to their general life courses. An autistic person with wealthy, supportive parents who push for hir to get appropriate supports at school and who have the time and money to give hir practical support into adulthood may go to university and end up becoming an academic or getting a well-paid job in a "geeky" industry with appropriate accommodations, while an autistic person with exactly the same cognitive abilities who is less privileged in terms of upbringing may end up with no school qualifications, unemployed, unsupported and on the streets or in an institution. Who's more likely to find a partner and get the opportunity to bear/conceive and raise children? (If the latter person does have a child, they may well be taken into "care" and either adopted by wealthier parents or end up institutionalised and unlikely to reproduce themselves.)

2) (although this may well be a bit chicken-and-egg) when it comes to "cultural" or "sociological" class, at least in English-speaking countries, autistic (or otherwise "odd") traits are *much* more accepted in upper/upper-middle class culture than in working-class culture. Someone who would be merely seen as "eccentric" (and possibly even admired for it) in a wealthy family/neighbourhood is much more likely to be bullied, ridiculed, maligned and pathologised in a poor family/neighbourhood, which tend to have much stricter norms of conformity (and often an explicit cultural association of, e.g., "nerdy" intellectualism or (especially in boys) "soft" or "effeminate" sensory sensitivity with being "posh" in a "not one of us", or even "class traitor", kind of way). Again, who's likelier to find a partner and have children?

(This reminds me: I really need to write about my own experiences of intersections between cultural class, gender and autism...)

I don't know how *much* of an effect reproductive selection would have on actual prevalence of autism in different social classes, or how the size of that effect would compare to the size of the "false" effect of differential access to diagnosis, but i would be surprised if the effect didn't exist at all.

Lindsay said...

Ooh, good points, Shiva!

Another thing I thought of reading your comment was that geek culture --- where a lot of autistic people first find they fit in, and meet potential friends/lovers --- is skewed pretty heavily middle-class and white. You (generic "you") might not feel as at home with other geeks if you're always feeling like you're not in on all the jokes --- like there's a lot of random cultural stuff you just don't get, because your background is so different from most other geeks'.

So that might also contribute to working-class autistics' finding it harder to find partners, too.

Ettina said...

Another genetic hypothesis:

As an autistic university student, I've been struck by two things.

Firstly, how much easier it is for me, with my kind of mind, to fit in and do well in university than in any other 'typical' setting I've been in so far.

And secondly, how many of my professors seem to have autistic traits.

So my hypothesis is that people who are in the area of BAP to HFA are likely to do well in university. In particular, they're more likely to have the kind of skill set where non-university career tracks (which often focus on service jobs, or on highly specialized motor skills, both areas that tend to be weaknesses for HFA/BAP people) are relatively limited for them, while at the same time their intense interests combined with average to high intelligence make them well suited to university. (Intense interests are an asset in that they allow you to pick a major more easily and focus more intently on studying for your major.) Therefore, HFA/BAP people may have a greater probability, relative to SES-matched NTs, of going to university and getting a degree. And this tends to increase the pay rate of the jobs you're qualified for. Now, HFAs are often underemployed relative to their education, but being BAP doesn't interfere as much with getting a job. So many BAPs would get jobs requiring university degrees, and therefore end up in a higher SES bracket. And they'd marry and have children, and those children would have a higher probability of autistic due to the parents' genetics.

Lindsay said...

Ettina, you also raise a good point.

I do not know how much of a guarantee that those of us who go to college ever do get jobs corresponding to our skill level, though --- one thing I encountered while researching employment issues in autism was the concept of "mal-employment", in which highly skilled, often college-educated autistic people are under-employed in menial jobs they are uniquely bad at, like the service jobs you mention in your comment! They do not last long at any one of these jobs, so they tend to have a string of them.

(For instance, I did terrifically in college but haven't gotten a single job offer since graduating seven years ago. I've pretty much given up on the idea of ever working in my field.)

However, your idea might very well hold true for BAP types who pass well and don't have much in the way of cognitive, motor or social impairment.