Carrefour S.A.

Shopping online may not save you anything

Shopping online may not save you anything

You find lower prices online than at bricks-and-mortar stores, right? Wrong.

Alberto Cavallo of the Massachusetts Institute of Technology displayed resourcefulness and ingenuity by producing a wide-scale international comparison of online and offline prices. He wanted to determine if prices collected online could be used to calculate inflation indices. After all, even in the U.S., the birthplace of e-commerce, where more than $200 billion of goods are sold online per year, that's less than 10 percent of the total retail volume. The global average is about 5 percent.

So how representative are online prices? Cavallo tried to find out with the help of two custom-made pieces of...