More on autism “clusters”

4 Feb

There are regions of California where the autism “rate” is much higher than in other regions. If you are a regular reader of this blog, you are likely thinking “repeat!” Yes, between Kev and myself and even the Evil Possum himself, David N. Brown, we have about 10 posts about the GMC ruling on Andrew Wakefield and the retraction of his article in The Lancet. Now another “autism cluster” post?

Only a month ago I blogged “Autism Clusters Found: areas with high incidence of autistic children“, discussing a paper by Dr. Hertz-Picciotto at the U.C. Davis MIND Institute. Well, it turns out that another “cluster” paper has been published. This article, The spatial structure of autism in California 1993-2001, is by Prof. Bearman’s group at Columbia. This is the same group that recently published Diagnostic change and the increased prevalence of autism

Here’s the abstract:

The spatial structure of autism in California, 1993-2001.

Mazumdar S, King M, Liu KY, Zerubavel N, Bearman P.

Institute for Social and Economic Research and Policy Columbia University, New York, NY, USA.

This article identifies significant high-risk clusters of autism based on residence at birth in California for children born from 1993 to 2001. These clusters are geographically stable. Children born in a primary cluster are at four times greater risk for autism than children living in other parts of the state. This is comparable to the difference between males and females and twice the risk estimated for maternal age over 40. In every year roughly 3% of the new caseload of autism in California arises from the primary cluster we identify-a small zone 20km by 50km. We identify a set of secondary clusters that support the existence of the primary clusters. The identification of robust spatial clusters indicates that autism does not arise from a global treatment and indicates that important drivers of increased autism prevalence are located at the local level

They used data from the California Department of Developmental Services (CDDS). This dataset has been discussed a lot online. While the work of Dr. Bearman’s group and Dr. Hertz-Picciotto’s group are both much more rigorous than the simple comparisons done by myself and others, there are severe limitations in using CDDS data. The CDDS does not make an effort to seek out all autistics, for one thing. There are variations by Regional Center in identification and services for disabled Californians.

That said, Prof. Bearman’s group found a large “cluster”. If a child was born in this region, he/she is about 4 times more likely to be listed by the CDDS with the label of autism than if he/she were born in the rest of California.

The cluster is in the Los Angeles area. (map was taken from the Wall Street Journal’s story, L.A. Confidential: Seeking Reasons for Autism’s Rise)

Prof. Bearman’s group checked that the cluster was stable over time and found that there was a region with the high administrative prevalence existed for 5 or more years. That is one good check that this is a “real” cluster and not a statistical artifact.

The Wall Street Journal quotes Prof. Bearman:

Dr. Bearman says he believes social influences are the leading cause for the high autism rates in Los Angeles, although the researchers continue to examine environmental issues.

Other studies have shown that older parents run a greater risk of having an autistic child. But when the Columbia researchers adjusted the Los Angeles cluster to factor out parental age, the higher levels remained. Dr. Bearman says he believes the high levels will also remain after the data are adjusted for education levels, socio-economic status and other demographic characteristics in future studies.

You may recall that the MIND Institute study found multiple “clusters”, using different criteria.

There is a cluster roughly centered on Hollywood in those maps, consistent with the newer Columbia study. (as an aside, the closeup map from the MIND Institute press release doesn’t look like the same region to me.)

It seems reasonable to assume that both groups were looking for clusters in a search for a possible “hot spot” of some environmental trigger for autism. Instead, Bearman’s group indicates “social issues” and Hertz-Picciotto’s group found parental education and proximity to autism treatment centers were linked to the “clusters”.

Both groups are to be commended, in my view. They are looking for some answers on causation. They are working with data that are much less than high quality, and they are dealing with shifting awareness and societal influences which could cloud any trends that may or may not exist.

9 Responses to “More on autism “clusters””

  1. Shannon Rosa February 4, 2010 at 07:46 #

    The MIND Institute maps are definitely odd — I live near one of the clusters:

    However all the kids with autism that I know live just outside the boundaries, and that includes two who have participated in MIND Institute studies. Also approximately 1/3 of the included area is an uninhabited island.

    Not really related to the study findings — I just take issue with poor cartography!

  2. Laurentius Rex February 4, 2010 at 13:03 #

    “They are working with data that are much less than high quality,”

    That is an understatement indeed. Some years ago I had somewhat over ambitiously considered putting together a book proposal looking at the “California epidemic” as a prime example of social construction, however I found that the data were too confused and erratic even to support that as a project.

    For those familiar with my blogging diatribes and who do not consider me an empiricist, I do have remind them that I am actually familiar with demographic and epidemiological data having in a past life researched such data in Coventry with a positive social outcome. However that was what you would call ‘action research’ rather than ‘academic research’ not that the paradigms for reliability should be any different for either.

  3. Joseph February 4, 2010 at 14:10 #

    That the LA RCs are “clusters” was something I talked about 3 years ago or so. People who work at CalDDS Data Request are well aware of this fact, as they have told me, and they have a graph of caseload growth by RC that they make available, which I’ve posted in my blog.

    There are some facts you probably won’t find in the literature just yet. For example, caseload growth in the LA RCs is slow compared to caseload growth in RCs with low administrative prevalence. This points to some RCs just being behind in their recognition of autism, and “catching up.”

    Additionally, RCs with high administrative prevalence tend to have a smaller proportion of autistics with MR. Conversely, RCs with a low administrative prevalence tend to have a high proportion of autistics with MR, with some exceptions. I show this here.

    About the data being “low quality,” that’s not an accurate characterization, in my view. If you want to know how many children in California are receiving services under the autism label, the data is very high quality, is it not? There’s probably little error in it. What is often “low quality” are the interpretations given to the data, e.g. when it is assumed that it tells you how many autistic children there are in California. So long as you don’t assume things like this, the data is perfectly fine, quite useful, and I don’t think there’s a comparable database.

  4. Jen February 4, 2010 at 16:24 #

    I wonder how much of it has to do with the high number of fertility clinics in and around the LA area? There’s certainly a higher incidence among higher-order multiple births (triplets plus), which also correlates to fertility interventions, which also correspond with parental age/income/education level.

  5. LAB February 4, 2010 at 16:26 #

    The presence of “Regional Centers” in California must definitely effect ASD diagnoses. I regularly talk to people out here on the east coast who have no idea where/how to get their child evaluated for ASD, and many of those kids remain undiagnosed at kindergarten and beyond. If we had a “Regional Center” up the road, I’m sure these kids would all have been seen/evaluated by age 3.

    As far as I know, the Regional Centers do free evaluations and even offer some treatment free of charge. That’s in direct contrast to other states, where some parents pay thousands of dollars to have their child evaluated, and thousands more for treatment. Considering the expense and the confusion about where to go, some parents avoid the medical evaluation and hope for the best. Some of those kids eventually get a school label of autism.

    I’m always curious to know how many kids receiving school-related services under the autism label in the US have a medical diagnosis of autism as opposed to just a school label. Are schools as qualified to diagnose ASD as medical specialists? I’d love to see the number of kids who have a medical diagnosis of ASD v. kids who have been labeled with ASD by the schools but have no official medical diagnosis. Not sure it really matters, but just curious.

  6. Joseph February 4, 2010 at 16:44 #

    I wonder how much of it has to do with the high number of fertility clinics in and around the LA area?

    That’s doubtful. How many children are born due to fertility treatment? It can’t be more than a small percentage. Someone would’ve noticed that most children born due to fertility treatments are autistic.

    Additionally, you’d find that West LA has a much higher prevalence than East LA. This is not the case.

    Again, treating these counts as full counts is what creates confusion and leads to failed hypotheses. This is a lesson that has to be learned at some point.

    Until it is shown that the regional differences are real, it would be best not to assume they are real. Alternatively, you can control for confounds like wealth, population density, awareness, etc. This might be valid to an extent, so long as the variables make sense (e.g. urbanicity is not a discrete variable, contrary to how Palmer et al. 2008 treats it) and the model is a good reflection of reality.

  7. Calli Arcale February 4, 2010 at 18:10 #

    There may actually be reason to implicate fertility treatment. Well, not the treatment itself, but the fact that people who need fertility treatment have fertility problems. Age, for one, which is already associated with an increased rate of developmental disorders in offspring. That factor alone may also account for some of the clustering, since affluent families tend to start having babies later in life (with or without assistance).

  8. livsparents February 4, 2010 at 21:40 #

    Actually these ‘clusters’ are centered around truckstops frequented by drivers delivering thimeresol to local vaccine manufacturing sites. It’s the only explaination aside from clouds from Chinese mercury tainted fires with GPS smart-delivery technology…

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