IN THE mall below a McDonald’s restaurant in Hong Kong, excitable children pose for photos next to a statue of the chain’s clownish mascot, Ronald, who lounges on a bench, one yellow glove raised in welcome. He fronts a display of other promotional decor, including a soft drink the size of a man and a box of fries that looms even larger. A video chronicles the chain’s 41 years in Hong Kong, which have been full of menu twists and tweaks: sausage McMuffins, shake-shake fries, chicken McNuggets, salads. At the restaurant upstairs, touchscreen menus now allow choosy customers to build their own burger, adding exotica like grilled champignon, herb aioli and sliced jalapeños or even (heresy!) subtracting the bun.

Innovation and differentiation—the creation of things new and singular—are a boon to economic progress and the bane of economic measurement. It would be much easier to compare economies across borders and time if goods remained much the same, wherever and whenever they were made. Fortunately, amid all the creativity and complexity, the Big Mac remains something of a constant. It varies rather little from country to country...Continue reading