## The Traveler’s Dilemma

Now for some real content. I came across this article in Scientific American about the Traveler’s Dilemma. To explain briefly, the TD is a game in which two players are each asked to select a number within certain boundaries (2 and 100, in the example). If both players select the same number, they are rewarded that number of points. (In the example, each point is worth $1, which makes the game of more than academic interest.) If one player’s number is lower, they are each awarded points equal to the lower number, modified by a reward for the player who selected the lower number and a penalty for the player who selected the higher number. So, for instance, if you choose (48) and I choose (64), you get 50 points and I get 46 points.

The intuition that I had upon reading the rules of this game was that it would be “best” for both players to choose (100). That is certainly true from a utilitarian point of view: (100, 100) results in the highest total number of points being given out – 200. The runners up are (99, 99), (100, 99), and (99, 100) with 198. However, there are two small problems – here’s the dilemma part – that prevent (100, 100) from being the “best” choice: one, the players are not allowed to communicate, and two, the (100, 99) and (99, 100) plays result in one player receiving 101 points – an improvement, for that player, over a 100 point reward.

So, the reasoning goes, if player one predicts that her opponent will play (100), she should play (99) in order to catch the 101 point reward. Her opponent, however, ought to use this same strategy, and also play (99), in which case player one ought to play (98) in order to trump her opponent, and so on and so forth. This reasoning degenerates to a play of the minimum number – in the example, (2). According to Basu, the author of the article, “Virtually all models used by game theorists predict this outcome for TD.”

However, reality does not follow these models. When people are asked to play the TD, many of them choose 100. Many of them choose other high numbers. Some seem to choose at random. Very few choose the “correct” solution – (2) – predicted by game theory. Something’s up.

Basu takes this to mean that all of our assumptions about rational behavior need to be questioned. With my philosophical background, I happen to have different assumptions about rational behavior than the mainstream, and so for me the results of the TD are not surprising in any way. But perhaps the best way to explain why the results to not surprise me is that I am a gambling man. Continue reading