## Sunday, December 12, 2010

### Game-theoretic board games

'Tis the season (almost) to sit around the fire playing board games and pretending to enjoy it. I recommend two board games, namely Poleconomy and Apocalypse, that I played a few times when I was a student; these came up in a conversation recently due to having some interesting game-theoretic content. I gave a talk at Microsoft Research (Cambridge) on Thursday, and Yoram Bachrach told me about the ripoff game, which has been played by human volunteers for cash prizes. Each individual game takes about one minute and works as follows. Each player is allocated a number, a fraction in the range [0,1] which is his “weight”. A subset of the players can form a winning team if their weights add up to at least 1. However, the winning team has not won the round until they have agreed on how to share the prize (worth 1 pound). For this purpose, each player gets to control another number in the range [0,1], which is the fraction of the prize that he requests from the winning team. And, the team does not win (and share the prize) until those fractions add up to at most 1. Apparently, the players sit in the same room but interact via computers, so the negotiation is somewhat stylized. Anyway, it turns out that Shapley value is quite a good predictor of the winnings associated with weights (although, there is variation from round to round, and some players are better at the game than others). A computational agent was implemented, which computed its Shapley value and then added 10%, and it performed well in competition.

This reminded me of an aspect of Poleconomy, a board game that simulates the interactions of politicians who happen to occupy corporate directorships “on the side”. (The game was developed in the early '80s.) From time to time, an “election” takes place, in which the players cast dice to determine the number of “votes” they obtain, and a Government may be formed by any subset of players who happen to have received a majority of the votes between them. There is some advantage to being in Government, so the immediate outcome of an election is a flurry of mental arithmetic and bargaining amongst the players to identify and agree upon a winning subset.

In Apocalypse, a player's move consists of a sequence of attacks. In each attack, the player chooses a number of units with which to attack another player, a whole number in the range 1...6, which is identified by placing a standard die with the chosen number uppermost underneath a cup; the player being attacked tries to guess the number. If the attacked player guesses correctly, that is the number of units that are lost by the attacking player; otherwise, the attacked player loses a single unit (and the attacking player gains a nuclear weapon, or part thereof, so there is an incentive to make lots of attacks.) Thus, each attack is a kind of generalized matching pennies, where the probability of choosing a smaller number is clearly larger than the probability of choosing a larger number, but all probabilities are positive.

Are there any other board games out there with interesting game-theoretic aspects?