EACH YEAR a typical American worker can afford more than six times as many Big Macs at home as a worker in Mexico can. That gap is the point of The Economist’s McWages index, which translates pay into burgers. Instead of relying on volatile exchange rates to compare salaries and affordability, the index shows how much of a familiar basket of goods the average paycheque can buy at local prices. The basket in question is the Big Mac: a global standard of patties, buns, cheese, onions, pickles, lettuce and sauce. The result is a back-of-the-greasy-napkin calculation of where salaries stretch furthest.