A trio of economists at Cornell and Indiana University-Purdue have done an as-yet-unpublished study that makes the following claims:
- As indicated by the Bureau of Labor Statistics’ American Time Use Survey, there's a correlation between local rainfall levels and amount of TV a young child watches.
- Comparing autism data and rainfall data in California, Oregon, and Washington (where rainfall levels vary substantially) reveals a correlation between autism rates and rainfall levels.
- Autism rates also correlate with "percentage of households that subscribe to cable television."
- Therefore, it's possible that watching a lot of TV before age 3 is "an important trigger for the onset of autism."
Gregg Easterbook of Slate wrote an article about this study a week ago, titled "TV Really Might Cause Autism." Turns out that Easterbrook had speculated that TV might cause autism back in early September; that piece was, as Easterbrook notes in the later article, "sheer speculation, since [he] knew of no researchers pursuing the question." So Easterbrook can be pardoned for being particularly interested in the Cornell study.
Apparently the second Easterbrook piece caused quite a stir online, though I missed that. Then, on October 20, along came a Time article: "A Bizarre Study Suggests That Watching TV Causes Autism." As you might expect from the title, Claudia Wallis (the article's author) doesn't take the Cornell study very seriously.
Wallis provides some useful background about the spike in reported autism rates in the past 35 years:
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[...]. 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 identical twin of a child with autism has only a 70% to 90% chance of being similarly afflicted.
(There are still plenty of people who claim that the cause is in fact vaccines and/or mercury, but according to the CDC, "The weight of currently available scientific evidence does not support the hypothesis that vaccines cause autism.")
The Time article goes on to take the new study to task for making such statements as "Our precipitation tests indicate that just under forty percent of autism diagnoses in the three states studied is the result of television watching due to precipitation" (in the study's abstract)--and I agree that using phrases like "result of" seems (as Wallis puts it) "oddly definitive." But the word "indicate" in the original sentence (left out by Wallis) makes it sound less definitive, and the study's actual conclusion says, among other things:
Although our findings are consistent with our hypothesis, we do not believe our findings represent definitive evidence for our hypothesis.
Wallis goes on to quote Vanderbilt University geneticist Pat Levitt as suggesting that rainfall could be producing other environmental factors, such as mold or mildew; the implication is that the study's authors didn't even think of that. In fact, though, the study does partly address that possibility:
[...S]ince precipitation is likely correlated with young children spending more time indoors generally, not just young children watching more television, our first main finding could be due to any indoor toxin. Therefore, we also employ a second instrumental variable or natural experiment, that is correlated with early childhood television watching but unlikely to be substantially correlated with time spent indoors.
If I'm understanding the study right (I haven't read the whole thing in detail), that sentence is talking about the cable-TV subscription levels part of the study. The authors later add:
[...I]t is theoretically possible that autism is positively correlated with cable subscription rates because young children in families with cable spend more time indoors and there is a toxin where exposure is higher for indoor activities than outdoor activities. But, although [that's] theoretically possible, we do not believe the effect of cable on time spent indoors by young children is likely to be large enough to [cause greater exposure to such a toxin].
Anyway, so the Time piece goes further than I think is warranted in attacking the study--when I started writing this entry, I was all set to say "Go read this great article in Time debunking this silly study," but then I looked at the study itself and saw that the authors are taking a much more reasonable and scientific approach than the Time article suggests. But the Time piece does end with some interesting stuff about relevant genetic issues, and notes that "[t]here are probably many routes to the disorder, involving diverse combinations of genes and noxious environmental influences."
Time has also published a brief response from Gregg Easterbrook to the Time article, in which Easterbrook notes that the Cornell study may result in someone doing a more definitive study that measures the issues directly rather than indirectly. (Side note: Easterbrook goes on to vaguely imply that, because Time Warner owns the Cartoon Network, Time may have had ulterior motives in "denouncing this research." I am very skeptical about this kind of conspiracy-theory finger-pointing; Easterbrook's use of this tactic makes me less inclined to trust him.)
Another interesting aspect of all this is that attributing autism to TV watching can be seen as yet another in a series of claims that one variety or another of bad parenting is the cause of autism. Kendra Pettengill of Oregon, a parent of an autistic child, discusses the "bad parenting" issue and provides some further criticisms of the study; I haven't read enough of the study to have an opinion on whether the authors anticipated those criticisms or not.
Do I have a point in all this? Not really. I think the study provides some very interesting correlations; I think some of the study's critics are underestimating and/or misunderstanding the study's authors; I think the study doesn't come close to addressing all the causes of autism (nor does it claim to); I think the study probably does oversimplify some things and ignore some relevant issues. And I should reiterate that the study has not yet been published, so I'm guessing it hasn't yet been peer-reviewed. But mostly, I just thought all this was an interesting topic and an interesting discussion.
(And since pretty much everyone I've seen comment on this study has their own axe to grind one way or another, I may as well grind my own, which is that claims that initially seem obviously silly, stupid, or counterintuitive often turn out to be much more reasonable when looked at in detail, beyond the surface level. On the other hand, sometimes such claims turn out to actually be silly or stupid when examined in detail; certainly I'm not claiming that silly-looking claims are always reasonable. (That would itself be both silly and unreasonable.) I'm just making my usual suggestion that people look beyond the surface before coming to conclusions.)