Perfect information

Perfect information is a concept in <a href="/facts/Game_theory/zkEIj1ya">game theory</a> and <a href="/facts/Economics/HYctA2Dn">economics</a> 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 than <a href="/facts/Complete_information/8jAPdVTW">complete information</a>, which implies <a href="/facts/Common_knowledge_(logic)/DwJ82TXM">common knowledge</a> 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 of <a href="/facts/Perfect_competition/les89UG3">perfect competition</a>. 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, a <a href="/facts/Sequential_game/kFPCl6VN">sequential game</a> 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 the <a href="/facts/Game/JNzato20">game</a> (e.g. the starting hands of each player in a card game).
Games where some aspect of play is hidden from opponents – such as the cards in <a href="/facts/Poker/bYSg9eCS">poker</a> and <a href="/facts/Contract_bridge/ohDtVpd9">bridge</a> – are examples of games with imperfect information.

Perfect information open-in-new

Perfect information