Perfect information is a concept ingame theory andeconomics that describes a situation where all players in a game or all participants in a market have knowledge of all relevant information in the system. This is different thancomplete information, which impliescommon knowledge of each agent's utility functions, payoffs, strategies and "types". A system with perfect information may or may not have complete information.
In economics this is sometimes described as "no hidden information" and is a feature ofperfect competition. In a market with perfect information all consumers and producers would have complete and instantaneous knowledge of all market prices, their own utility and cost functions.
In game theory, asequential game has perfect information if each player, when making any decision, is perfectly informed of all the events that have previously occurred, including the "initialisation event" of thegame (e.g. the starting hands of each player in a card game).[1][2][3][4]
Games where some aspect of play ishidden from opponents – such as the cards inpoker andbridge – are examples of games withimperfect information.[5][6]
Chess is an example of a game with perfect information, as each player can see all the pieces on the board at all times.[2] Other games with perfect information includetic-tac-toe,Reversi,checkers, andGo.[3]
Academic literature has not produced consensus on a standard definition of perfect information which defines whether games with chance,but no secret information, and games withsimultaneous moves are games of perfect information.[4][7][8][9]
Games which aresequential (players alternate in moving) and which havechance events (with known probabilities to all players) butno secret information, are sometimes considered games of perfect information. This includes games such asbackgammon. However, some academic papers do not regard such games as games of perfect information because the results of chance themselves are unknown prior to them occurring.[4][7][8][9]
Games withsimultaneous moves are generally not considered games of perfect information. This is because each player holds information, which is secret, and must play a move without knowing the opponent's secret information. Nevertheless, some such games aresymmetrical, and fair. An example of a game in this category isrock paper scissors.[4][7][8][9]
