Dictionary :: Games

Glossary of game theory terms.

Rock Paper Scissors

Scenario

To determine who is required to do the nightly chores, two children simultaneously make one of three symbols with their fists - a rock, paper, or scissors. Simple rules of "rock breaks scissors, scissors cut paper, and paper covers rock" dictate which symbol beats the other. If both symbols are the same, the game is a tie. Similar to the two-strategy Matching Pennies game.

Description

The game is zero sum. The only equilibrium is in mixed strategies. Each plays each strategy with equal probability, resulting in an expected payoff of zero for each player.

Example

Child 2
rock paper scissors
Child 1 rock 0,0 -1,1 1,-1
paper 1,-1 0,0 -1,1
scissors -1,1 1,-1 0,0

General Form

Player 2
L C R
Player 1 U a,r b,u c,x
M d,s e,v f,y
D g,t h,w i,z
Where the following relations hold:
c = d = h = -b = -f = -g; a = e = i = 0
t = u = y = -s = -w -x; r = v = z = 0

updated: 12 August 2005
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