Is organic food little more than a trumped-up marketing scheme, another way for affluent consumers to waste money? A just-released paper by Stanford researchers—and the reaction to it by the media—suggests as much. (Abstract  here; I have a copy of the full study, but can’t upload it for copyright reasons.)
“Stanford Scientists Cast Doubt on Advantages of Organic Meat and Produce,” declared  a New York Times headline. “Organic food hardly healthier, study suggests,”announced  CBS News. “Is organic healthier? Study says not so much, but it’s key reason consumers buy,” The Washington Post grumbled .
In reality, though, the study in some places makes a strong case for organic—though you’d barely know it from the language the authors use. And in places where it finds organic wanting, key information gets left out. To assess the state of science on organic food and its health benefits, the authors performed what’s known among academics as a “meta-analysis”—they gathered all the research papers they could find on the topic dating back decades, eliminated ones that didn’t meet their criteria for scientific rigor, and summarized the results.
In another post I’ll get to the question of nutritional benefits—the idea, expressed by the Stanford authors, that organic and conventional foods are roughly equivalent in terms of vitamins and other nutrients. What I want to discuss now is the problem of pesticide exposure, and why I think the Stanford researchers are underestimating the risks.
In short, the authors’ findings confirm what the Environmental Working Group, working from USDA data, has been telling us for years : that organic fruits and vegetables harbor significantly fewer pesticide residues than their chemically grown peers. Summing up the evidence of the studies they looked at, the Stanford researchers find what they call a 30 percent “risk difference” between organic and conventional food—which to the mind not trained in statistics, sounds like organic foods carry 30 percent less risk of exposing you to pesticides. And they immediately undercut that finding by noting that the pesticide traces found in both organic and conventional food tend to be at levels lower than the Environmental Protection Agency’s maximum allowed limits. Takeaway: Conventional produce carries trivially small levels of pesticides, and you might as well save your money and forget organic.
What’s wrong with this comforting picture?
1. Conventional produce is much worse than organic on the pesticide-exposure question than the 30 percent number suggests. That’s what Chuck Benbrookof the Organic Center shows in a detailed critique of the study . To get the 30 percent number, the authors used an odd statistical construct they call “risk difference.” By their method, if 5 percent of organic vegetables contain at least one pesticide traces and 35 percent of conventional vegetables contain at least one trace, then the “risk difference” is 30 percent (35 minus 5). But that’s a silly way of thinking about it, because there’s a much greater difference between those numbers than 30 percent. Crunching the authors’ own raw data, Benbrook finds “an overall 81% lower risk or incidence of one more pesticide residues in the organic samples compared to the conventional samples.”
But even that doesn’t get to the full extent of the study’s underestimation, since: