University of St. Gallen
Rock, Scissor and Paper
Behavioral Game Theory
Rachmartika Astarini – 10600823
The child’s play of Rock, Scissor and Paper is in fact played in most of the world. Whatever its name, children aren’t the only ones to play it. Adults have also been known to use it when they cannot agree or would rather leave a decision to chance. And there are numerous articles that discuss the game theory within this game. a. History
Japan invented jankenpon in 19th century. Ken literally means fist. Some believes that this game is actually originated from China in Han Dynasty. Then on the 20th, it is known worldwide. Rock Paper Scissor is not only a child play, even adults play it. When they have to choose something and they want to let the chance choose, this Rock Paper Scissor game is mostly used. Rock Paper Scissor comes with different names across countries. Rochambeau is one of the names of this game. This name originated from the story of George Washington playing the Rock Paper Scissor game with Lord Comwallis and the Comte de Rochambeau to decide who would be the last to leave Comwallis’s tent after signing of British surrender at Yorktown in 1781. The story goes that Rochambeau won, explained the originality of the name. * Varieties
Rock, Scissors and Paper played by all people from all over the world though under various names. In some place, they even have different rules with addition of gesture, such as the Rock, Paper, Scissors, Lizard, and Spock game mentioned back in 2005. In some country they have the exact three gestures but with different character. In Indonesia for example, people used the character of Earwig – Elephant – and Men, with almost the same rule. Snake – Frog - Slug for Japanese, Bear – man – Gun for Canada, and Bear – Cowboy – Ninja may be specific to Milwaukee. * World play
The world play it so they have the rules standardized. The so-called World Rock, Scissor and Paper Society or WRSPS is the organization engaged to all the standardization of rules and international competition. Oh yes… They have the international championship for this game. In fact, they have many of them, such as USA Rock Paper and Scissors League, UK Rock Paper and Scissors Championship, and the world series of Rock Paper and Scissors Game. One of the competitions also listed in Guinness World Book of Record for having the biggest number of participants, reaching 6500 participant on 9 July 2010, including children and adults. The WRSPS also did some research on players’ behavior and they collect the statistics of each tournament participants.
Rules and matrix
The focus in this paper will be the two-player game. The players hold their right hands out simultaneously at an agreed signal to represent a rock (closed fist), a piece of paper (open palm), or a pair of scissors (first and second fingers held apart). If the two symbols are the same, it’s a draw. Otherwise rock blunts scissors, paper wraps rock, and scissors cut paper, so the respective winners for these three outcomes are rock, paper, and scissors. It’s dead easy! The rules are simple, but the game itself is as complex as mind of your opponent. If both players choose the same gesture, the game is tied and the players throw again. The game is over only when one player WINS…
Rock, Paper, Scissors is a zero-sum game. If you count a win as +1 point, a loss as –1 point, and a draw as zero, for example, the sum of the wins, losses, and draws for a game is always zero. To a game theorist this means just one thing—the optimum strategy can be worked out from the Minimax principle. This leads to the intuitively obvious conclusion that the best approach, in the absence of any information about the opponent’s intentions, is to use a mixed strategy, throwing rock, paper, and scissors at random, with equal probability for each, resulting in an expected payoff of zero for each player. A mixed...