Some of you might be familiar with the Big Mac Index, an index calculated by The Economist that compares the prices of Big Macs across countries (see Economist BMI Page). The underlying idea is that, by comparing the relative cost of Big Macs, we can get a sense for whether exchange rates appropriately equalize the prices of goods across countries in the manner suggested by Purchasing Power Parity (PPP) theory. If the price of Big Macs is not equivalent across countries, some take that to suggest that currency exchange rates are out of whack – i.e., one currency is overvalued while the other is undervalued.
Irrespective of what you believe about the Big Mac Index – whether you think it truly is indicative of exchange rate imbalances, or simply exposes shortcomings of PPP theory – it has gained currency amongst economists, though admittedly, mostly as a humorous diversion.
Nevertheless, Benn Steil and Dinah Walker, bloggers at the Council on Foreign Relations, offer an “updated” version of such an index by examining the relative prices of a product that they argue is likely to be more homogenous from country to country – the Apple iPad Mini (click on the figure below to see a larger image, or visit CFR iPad Mini Index for the full story).
Compared side-by-side, the Big Mac and iPad Mini indexes differ markedly. So who has it right? Or is this just further evidence that PPP theory needs to be revisited?