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February 24, 2009
Reporters Confuse Two Big Words: 'Causation' and 'Correlation'
Eating ice cream causes shark attacks. Don’t believe us? How else to explain the fact that both ice cream sales and the rate of shark attacks have been increasing at the same time? Okay, we’re kidding. They’re obviously not related. But we couldn’t help ourselves when we read a breathless headline from ABC News: “Living Near Fast Food Ups Stroke Risk.”
ABC reported on a study that was presented at the International Stroke Conference in San Diego last week. The University of Michigan study, “Fast Food and Stroke Risk,” was not among the 195 pieces of research given oral presentations at the conference. (Read the study’s abstract here, on page 86.)
But what if the authors of the study had been permitted to subject their core finding -- “a significant association between fast food restaurants and stroke risk” -- up for discussion? They would have had to answer some tough questions, the kind we noticed that ABC News didn’t ask.
For example: How much weight should be given to research based on a single community (Nueces County), in a single state (Texas), in a short time period (between January 2000 and June 2003)? Is that an accurate representative of all of America, all of the time?
And the study's central idea? It's not exactly a medical-milestone home run. Buried deep in ABC's coverage is the mother of all disclaimers from the lead author of the study, Dr. Lewis Morgenstern:
But he cautioned that the findings are purely associative and do not necessarily point to a direct link between the restaurants' offerings and potentially deadly stroke.
"I can't tell you that anybody who had a stroke in this study has ever had a burger in their lives," Morgenstern said. "But I can tell you that these neighborhoods on the whole have factors that increase the risk of stroke."
Keith Thomas Ayoob, a pediatric nutritionist at the Albert Einstein College of Medicine in Brooklyn, N.Y., agreed that the results of the research did not lend themselves easily to an interpretation that fast food was the true stroke culprit.
"It's hard to know whether this is a chicken or egg thing," he said.
Morgenstern posed some even more provocative questions in an interview with Reuters: “Is it direct consumption of fast food? Is it the lack of more healthy options? Is there something completely different in these neighborhoods that is associated with poor health?”
To which, we might add: "Is it a lack of exercise in Nueces County, or a high smoking rate?" These are all good questions. Too bad most reporters aren’t asking them.
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