Prices for many goods do not move the way economists think they should


TWO YEARS ago British chocoholics felt the pinch from the decision to leave the European Union. As sterling tumbled, global firms selling to the British market faced the same production costs as before, but got less money for each sweet sold. Rather than raise the price per chocolate, some chose to shrink the chocolate per price. The famous peaks on a bar of Toblerone grew conspicuously less numerous (though Mondelez, the bar’s maker, said Brexit was not the cause). Other products suffered the same “shrinkflation”: toilet rolls and toothpaste tubes became smaller. The threat of Brexit made the phenomenon more visible, but it is surprisingly common. Statisticians and policymakers need to take note.

Every first-year economics student quickly becomes familiar with charts of supply and demand, which place price on one axis and quantity on the other. Given a drop in demand, the charts show, firms can either sell fewer items at the prevailing price or cut prices to prop up sales. But online retailing, which makes it easier to collect fine-grained price data, reveals how poorly textbook models reflect real-world market dynamics. The prices of consumer goods, it turns out, behave oddly.