Childhood vaccines, toxins, genes and now television watching? The alarming rise in autism rates is one of the biggest mysteries of modern medicine, but it's irresponsible to blame one factor without hard scientific proof.
Strange things happen when you apply the statistical methods of economics to medical science. You might say you get dismal science, but that's a bit glib. You certainly get some strange claims-like the contention of three economists that autism may be caused by watching too much television at a tender age. It gets stranger still when you look at the data upon which this argument is based. The as yet unpublished Cornell University study, which will be presented Friday at a health economics conference in Cambridge, Mass., is constructed from an analysis of reported autism cases, cable TV subscription data and weather reports. Yes, weather reports. And yet, it all makes some kind of sense in the realm of statistics. And it makes sense to author Gregg Easterbrook, who stirred the blogosphere this week with an article about the study on Slate, provocatively (and perhaps irresponsibly) titled "TV Really Might Cause Autism."
The alarming rise in autism rates in the U.S. and some other developed nations is one of the most anguishing mysteries of modern medicine-and source of much desperate speculation by parents. In 1970, its incidence was thought to be just 1 in 2,500; today about 1 in 170 kids born in the U.S. fall somewhere on the autism spectrum (which includes Asperger's Syndrome), according to the Centers for Disease Control and Prevention. Some of the spike can be reasonably attributed to a new, broader definition of the disorder, better detection, mandatory reporting by schools and greater awareness of autism among doctors, parents and educators. Still, there's a nagging sense among many experts that some mysterious X-factor or factors in the environment tip genetically susceptible kids into autism, though efforts to pin it on childhood vaccines, mercury or other toxins haven't panned out. Genes alone can't explain it; the identicial twin of a child with autism has only a 70% to 90% chance of being similarly afflicted.
Enter Michael Waldman, of Cornell's Johnson Graduate School of Management. He got to thinking that TV watching-already vaguely associated with ADHD-just might be factor X. That there was no medical research to support the idea didn't faze him. "I decided the only way it will get done is if I do it," he says. Waldman and fellow economists Sean Nicholson of Cornell and Nodir Adilov of Indiana University-Purdue, were also undeterred by the fact that there are no reliable large-scale data on the viewing habits of kids ages 1 to 3- the period when symptoms of autism are typically identified. They turned instead to what most scientists would consider wildly indirect measures: cable subscription data (reasoning that as more houses were wired for cable, more young kids were watching) and rainfall patterns (other research has correlated TV viewing with rainy weather).
Lo and behold, Waldman and colleagues found that reported autism cases within certain counties in California and Pennsylvania rose at rates that closely tracked cable subscriptions, rising fastest in counties with fastest growing cable. The same was true of autism and rainfall patterns in California, Pennsylvania and Washington state. Their oddly definitive conclusions: "Approximately 17% of the growth in autism in California and Pennsylvania during the 1970s and 1980s was due to the growth of cable television," and "just under 40% of autism diagnoses in the three states studied is the result of television watching due to precipitation."
Result of? Due to? How can these researchers suggest causality when no actual TV watching was ever measured? "The standard interpretation of this type of analysis is that this is cause and effect," Waldman insists, adding that the 67-page study has been read by "half-a-dozen topnotch health economists."
Could there be something to this strange piece of statistical derring- do? It's not impossible, but it would take a lot more research to tease out its true significance. Meanwhile, it's hard to say just what these correlations measure. "You have to be very definitive about what you are looking at," says Vanderbilt University geneticist Pat Levitt. "How do you know, for instance, that it's not mold or mildew in the counties that have a lot of rain?" How do you know, for that matter, that as counties get more cable access, they don't also get more pediatricians scanning for autism? Easterbrook, though intrigued by the study, concedes that it could be indoor air quality rather than television that has a bearing on the development of autism. On a more biological level there's this problem, says Drexel Univeristy epidemiologist Craig Newschaffer: "They ignore the reasonable body of evidence that suggest that the pathologic process behind autism probably starts in utero"-i.e., long before a baby is born.
The week also brought a more definitive, though less splashy finding on the causes of autism, published in the Proceedings of the National Academy of Science. A team led by Levitt found that a fairly common gene variation-one that's present in 47% of the population-is associated with an increased risk of autism. People with two copies of the gene have twice the average risk of autism; those with one copy face a slightly increased risk. The gene is intriguing because it codes for a protein that's active not only in the brain-the organ most affected by autism-but also in the immune system and the gastrointestinal tract, two systems that function poorly in many people with autism. Levitt estimates that anywhere from five to 20 genes may underlie the vulnerability to autism. There are probably many routes to the disorder, involving diverse combinations of genes and noxious environmental influences. Could Teletubbies be one of them? Conceivably, but more likely the trouble starts way before TV watching begins.
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