Invisible Gorilla

The link between advertising and obesity may not be all that it appears to be, write Christopher Chabris and Daniel Simons in The New York Times (3/10/13). Christopher and Daniel, co-authors of The Invisible Gorilla: How Our Intuitions Deceive Us, question a study in which researchers reported a link between the preponderance of outdoor ads for food and obesity. The researchers first recorded every outdoor ad they saw “in 228 census tracts around Los Angeles and New Orleans,” and then telephone surveyed the locals, “paying them to report their height, weight and other information.”

Based on this data, the researchers concluded: “For every 10 percent increase in food advertisements, the odds of being obese increased by 5 percent.” The flaw in this conclusion, Christopher and Daniel argue, is the assumption “that any link between obesity and advertising occurs because more advertising causes higher rates of obesity. But the study at hand showed only an association: people living in areas with more food ads were more likely to be obese than people living in areas with fewer food ads.” In other words, the study captured the “what” of the situation but not the “why.”

It could be simply that food marketers tend to place their outdoor ads in neighborhoods where plumposity prevails — not unlike the way luxury retailers tend to put stores in wealthier locales. “A superior method,” according to Christopher and Daniel, “would be to restrict food ads temporarily in a randomly selected set of areas, and then compare the prevalence over time of obesity in those areas and the nonrestricted ones.” Such a test would not be easy to implement, but would help provide evidence of a cause of obesity, not just an association with it.