What Is Imperfect Information in Game Theory?


Martha Robinson

In the world of game theory, “imperfect information” refers to a situation where players do not have complete knowledge about the game they are playing. This can include not knowing certain rules, not knowing what moves their opponents have made, or even not knowing who their opponents are.

When there is imperfect information in a game, it can have a significant impact on the strategies that players employ. In this article, we will explore what imperfect information means in game theory and how it affects gameplay.

What is Game Theory?

Before diving into the concept of imperfect information, let’s first define what game theory is. Game theory is a branch of mathematics that studies how people make decisions in situations where their outcomes depend on the decisions of others. It provides a framework for understanding strategic interactions between individuals or groups.

Game theory has applications across many fields, including economics, political science, biology, and psychology. It has been used to model everything from auctions to international conflicts and is an essential tool for understanding human behavior.

Perfect Information vs. Imperfect Information

In game theory, there are two types of information: perfect and imperfect. Perfect information means that all players know everything about the game they are playing – including the rules and all previous moves made by all players.

On the other hand, imperfect information means that one or more players do not have complete knowledge about the game. This can happen for many reasons – perhaps some rules were not explained clearly, or maybe a player missed some critical piece of information about their opponent’s strategy.

Imperfect information can be further divided into two categories: incomplete and asymmetric. Incomplete information refers to situations where all players lack certain information about the game; asymmetric information refers to situations where some players have more knowledge than others.

Examples of Imperfect Information

Let’s consider an example to illustrate how imperfect information works in practice. Imagine that you are playing a game where you have to guess the number that your opponent is thinking of between one and 100.

In this case, if your opponent tells you whether your guess is too high or too low after each turn, then you have perfect information about the game. You know all the rules, and you know how your opponent is responding to your moves.

However, if your opponent keeps their responses vague or doesn’t respond at all, then you have imperfect information about the game. You don’t know whether you’re getting closer or farther away from their number, and this lack of information can impact the strategy that you employ.

Another example of imperfect information is poker. In poker, players don’t know what cards their opponents are holding. This lack of knowledge can lead to players bluffing or making unexpected moves based on incomplete information.

Impact on Strategy

When there is imperfect information in a game, it can make it more difficult for players to make optimal decisions. Players must rely on assumptions and probabilities to make decisions instead of having complete knowledge.

This uncertainty can lead to interesting gameplay dynamics. For example, in a game with incomplete information, players may need to spend time trying to gather more information before making a move. In contrast, in a game with asymmetric information, one player may try to exploit their superior knowledge by misleading their opponents or using unexpected strategies.


Imperfect information is an essential concept in game theory that has far-reaching implications for strategic decision-making. When there is imperfect information in a game, it can lead to unexpected gameplay dynamics and require players to employ different strategies than they would in games with perfect information.

Understanding imperfect information is crucial for anyone interested in game theory or strategic decision-making. By considering this concept and its implications carefully, players can gain an edge over their opponents and improve their chances of success in games of all kinds.