Romaine Lettuce

We've all heard the phrase associated with the way in which the media covers stories: "If it bleeds it leads!" There doesn't have to be any blood in the picture for the media to sensationalize, avoid any contextual information that would mitigate concern, or otherwise provide a counterpoint to the immediate narrative.

Unless you were traveling in Outer Mongolia over the Thanksgiving holiday, you heard the breathless warning (originating with the CDC) to avoid eating Romaine lettuce. There was an outbreak of E. coli 0157:H7 that infected 43 people across the United States. The outbreak was serious and as a consequence of the warning, the entire Romaine lettuce industry came to a halt. Tens of millions of dollars were lost.

But was an outright ban on eating Romaine lettuce justified? Maybe a warning that included information discussed by Jim Prevor would have been appropriate:

The U.S. population is about 326 million. If 47% of the population eats romaine each week [based on polling], that’s about 153 million people. We know of 43 people who have been infected with E. coli from romaine lettuce. According to the CDC, illness start dates range from Oct. 8 to Oct. 31—a period of about three weeks. If we assume, conservatively, that each of those 153 million people eats one serving of romaine each week, then we can figure there were 459 million servings consumed during the three weeks the infection was being transmitted.

This means the odds that eating a serving of romaine will make you sick are about 1 in 11 million, and the odds it will put you in the hospital are less than 1 in 28 million. To put this in perspective, the probability of getting a royal flush in poker is dozens of times as great, at 1 in 649,740, and the probability of an amateur hitting a hole-in-one in golf is hundreds of times as great, at 1 in 12,000. If you are that risk-averse, you should stay away from dogs—the lifetime odds of getting killed by a dog attack are about 1 in 112,000. Even the odds of getting struck by lightning in a particular year are higher than 1 in a million.

To put it another way: If this outbreak were active every day, and you ate one salad a day, on average you would be hospitalized for E. coli once every 77,000 years.

Those of us who are numerate and try to think critically already understood this and smiled as we listened to friends and neighbors obsess over the last time they ate Romaine lettuce and whether they were at risk.

The problem is that this kind of thinking, along with the the damage it does, pervades the media and the general public. There's not much that can be done about it because context is rare in modern media coverage and innumeracy among the public is rampant.