Keynes and the problem of queue in Supermarkets

photo credit - steve crane on Flickr

That's a universal problem for every customer : after having spend much time (too much time) in the store, looking for all the needed (and unneeded) products, it's now time to pay.

And the question is : which check out will be the fastest ?

Economists have tried to analyze the situation with the Random Walk theory, a mathematical formalisation of random elements. Complicated studies for a simple result : there is no answer !

Why ?

Well, if people had a way to find the fastest line, most of the customers would join it and it would not be the fastest line any longer... This is the same principle John Maynard Keynes refered to when he described how does the stock market works in his General Theory of Employment, interest and money . Keynes compared the stock market to a beauty contest where people were invited to choose the nicest girl (that kind of contest were very popular at that time). The winner is the one who choses the girl closest to the general opinion.

As Keynes writes : "it is not a case of choosing those which, to the best of one's judgement, are really the prettiest, nor even those which average opinion genuinely thinks the prettiest. We have reached the 3rd degree where we devote ou intelligences to anticipating what average opinion expects the average opinion to be. And there are some, I believe, who practice the 4th, 5th and higher degrees."

That's why when you've chosen the "seems to be" fastest line, it becomes to slow down...

From my own experience, when all lines are very busy, you may find a better way at the extremities, especially the closest line from the entrance, as people tend to finish their shopping circuit at the other side of the store. But that's a very empiric method.

Other tip from personal experience: pretty cashier girl usually get more cash at the end of the day (attracting more men clients ?). So choose the not so attractive ones for a fast check out !(Sorry, no photos for that point...).

Next post : how does Disney manage extremely well the queue problem...

Example of Beauty Contest for 1953 (Keynes wrote his theory in 1936)