To get information about environmental factors (which the study laments are “mostly undocumented”) they used an interesting proxy: diagnoses for male genital malformations. Specifically, if an area had a high rate of these kinds of malformations—micropenis, for example, or another disorder called hypospadias—that suggests possible environmental toxins in the area, like lead or pesticides, the study says. As Rzhetsky tells Newsweek, “The idea of the study is to use malformation rates in newborn boys as the canary in the coal mine.” (It was just published in PLOS Computation Biology.)
They also incorporated a large amount of other data, including income levels, ethnicity, the amount of viral infections reported, whether an area is urban or rural, and state diagnostic standards. Their conclusions were unequivocal: the greater amount of malformations in boys, the greater the autism rates in the area, suggesting a correlation between environmental factors and autism diagnoses. In fact, the study reports “an increase in ASD incidence by 283% for every percent increase in the incidence of malformations” in males. Rzhetsky says he was surprised—he didn’t expect the correlation “to be so profound.”
That wasn’t all they found. For example, states with stricter diagnostic standards had a lower amount of ASD diagnoses. In addition, income levels affected autism diagnoses — slightly. As income level went up, so to do diagnosis rates for ASD and ID, but not by much. That’s probably because wealthier families have access to more accurate diagnoses, Rzhetsky suggests.
Some autism experts express skepticism about what the study really shows. “I’m not so impressed,” says Eric Fombonne, a professor at Oregon Health & Science University and an autism researcher who focuses on its epidemiology. His biggest problem with the study falls under what can be called “the ecological fallacy”—basically that correlation is not the same thing as causation, especially when looking at the big picture. For instance it would be a fallacy to assume that just because alcoholism rates are high in a place with high suicide rates, that one is causing the other.
Fombonne also faulted the study for several methodological shortcomings. “The fact they have this significant association [between malformation and autism rates] increases my suspicions of ecological fallacy, because it makes no biological sense at all,” he says.