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.