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What has been the real driver of violent crime in America? Not unemployment, or guns, or wealth disparities, or lack of access to education. According to a fascinating new Mother Jones article, it’s exposure to lead.

The piece builds a case around this thesis: “Gasoline lead is responsible for a good share of the rise and fall of violent crime over the past half century.” This isn’t totally crazy, since we know that lead is a destructive neurotoxin. But any skeptic out there would immediately wonder about the evidence behind such an encompassing claim, mainly because it rests mostly on population-level observational studies, which look at links between lead exposure in the environment and crime rates. As Dr. David Juurlink, a physician and researcher at the Sunnybrook Health Sciences Centre, told Science-ish, while lead could be the missing element in violent crime, “Many, many other factors also could, particularly in concert. Perhaps lead is one contributing factor, but it’s an abuse of the basic tenets of epidemiology to ascribe so much of the blame to lead.”

In other words, he added, a correlation between the two phenomena does not equal cause-and-effect.

Almost as soon as the article was published, debunkers were out in full force, picking apart the evidence behind the story. Even the author of the article, Kevin Drum, followed up with a blog post outlining the different types of evidence in the piece and the need for further research. But many a reader may have left the article thinking that the lead theory is more than just a theory; that it’s the little-known cause of criminal activity.

And it’s not the last, or even most offensive, article that will contain an incredible thesis about new science. So how do you avoid falling prey to bad science in health stories? This is a question Science-ish gets asked a lot, most recently related to an article published in Slate about Dr. Oz’s dubious use of medical evidence. Understanding evidence-based medicine and statistics takes years of practice and study, but the good news is there are a few very basic red flags to keep in mind when you’re reading about the health sciences.

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