How do you choose the shortest queue in the supermarket?


My typical Friday evening is spent grocery shopping. And since it's start of the weekend, half the world is out there doing the same. Imagine there are 5 cashier counters and 5 equally long queues. How do you choose which queue to join?

If I was a mathematician, I would tell you how all the odds are stacked against you. If you join a random queue, there are four other queues with a 4/5 chance of being faster than your queue.

We economists view the world slightly differently. The efficient market hypothesis states that you can never outperform a random choice of shares because public information is immediately incorporated in the prices. In this context, if any queue is really the quickest, people would have already joined it, nullyfing any advantage it may have.

In reality, markets aren't efficient and it is possible for a well informed decision maker to beat the market. But In a supermarket, very few have much to gain by being expert queuers. Moreover there are other considerations like proximity to queue, preference to a particular cashier, card versus cash counters and dedicated alcohol counters, that makes it ineffecient.

Thus beating a supermarket queue isn't that easy. It requires complex calculations based on queue size, items per queued customer, cashier's processing competency, mode of payment etc. So is it worth it? For a few saved minutes.

I will leave that to you. Happy shopping!