It’s always tempting to switch lines in the supermarket. After waiting for 5 minutes inÂ one checkout line yesterday, Gweneth and I jumped to the next queue. Turned out we’d jumped in behind someone who was complaining about a price being wrong, and the ensuing price check cost us an additional 15 minutes.
At some point during that 15 minutes, it struck me. The efficient markets hypothesis tells us that (a) a stock’s price reflects all publicly available information (management skill, product demand, etc), (b) the best way of making money in stocks is to buy a slice of the stockmarket and sit tight, (c) churning your portfolio is likely to be inefficient.
So if we believe shoppers are as rational as traders (why not?), then there should be a parallel efficient supermarkets hypothesis. The efficient supermarkets hypothesis tells us that: (a) the length of the line reflects all available information about its speed (cashier skill, size of preceding trolleys etc), (b) the best way of getting through the supermarket checkout is to pick the closestÂ line and stay in it, and (c) the worst thing you can do at the supermarket is switch lines.
Update 1: Joshua Gans prefers to think of this through the lens of auction theory, andÂ offers his own deux et machina – get your child to cry.Â
Update 2: A phone conversation with JG just now convinced me that I needed to be clearer in my exposition.Â The argument is this: if your fellow shoppers are rational, then there is no clever strategy that can get you out of the door faster. Just pick the nearest queue (or, if you want to take Russell’s advice, the queue with the nicest-looking shoppers), and stick in it.
Update 3: Harry Clarke’s view.