Grocery Store Science

Dan Meyer, like most people, has long wondered whether there was a good way to predict which check-out line at the grocery store will be the fastest. Unlike most people, he used science to find an answer: “I spent ninety minutes last week just watching, counting, and timing groceries as they slid across a scanner.” This produced a graph showing a roughly linear relationship between items in a cart and time spent checking out.

The conclusion: Each item adds 2.9 seconds on average, but each person adds 48 seconds on average. So you would rather be on line behind one person with a full cart than three people in the express line. Also, contrary to what those annoying Visa commercials say, paying with cash is faster than credit.

This project and the resulting blog post got Meyer a segment on the evening news, in which he explains the basic results, and “races” a reporter through the checkout line several times. What’s more, it’s actually a pretty good report– short and a little silly, but it gets the basic point across clearly and effectively. Funny what it takes to get good science in the media.

(Just to be perfectly clear, I’m not laughing at Meyer for doing the piece– I’ve been on the local news three times, one of them to talk about how gasoline expands when it’s hot, so I have no standing to make fun of him for checkout-line racing.)

(The other two times were more serious– a piece on a summer program for students from disadvantaged backgrounds, and one on a class about the 2004 election. From this, I know that it’s kind of tricky to be interviewed by somebody off camera– I have a tendency to look off to the side, up in the air, or basically anywhere but the lens…)