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Game Theory and the Nash Equilibrium

Nobel prize-winning mathematics genius John Nash of Princeton University works through his notes on game theory at the University of Hong Kong. 18 February 2003
Nobel prize-winning mathematics genius John Nash.

South China Morning Post / Getty Images

Game theory is the study of how and why players make decisions about their circumstances. Using game theory, real-world scenarios for such situations as pricing competition and product releases can be laid out and their outcomes predicted. Companies may use game theory to determine the 澳洲幸运5官方开奖结果体彩网:Nash Equilibrium and see the benefit in their budgeᩚᩚᩚᩚᩚᩚ⁤⁤⁤⁤ᩚ⁤⁤⁤⁤ᩚ⁤⁤⁤⁤ᩚ𒀱ᩚᩚᩚting or pricing strat♉egies.

Key Takeaways

  • Game theory is the study of how and why players make decisions.
  • Nash equilibrium helps a player determine the best payoff based not only on their decisions but also on the decisions of other parties involved.
  • Companies can use game theory to predict the outcomes of pricing competition and product releases.

Whose Turn Is It?

Proponents of 澳洲幸运5官方开奖结果体彩网:game theory often tabulate the different outcomes in what is called a matrix. While sequential games are played by turn, simultaneous games are played with each player making their decision at the same time. With simultaneous games, participants no longer use the common introductory method of 澳洲幸运5官方开奖结果体彩网:backward induction.

Player one / Player two Left Right
Up (1, 3) (4, 2)
Down (3, 2) (3, 1)

This matrix is referred to as normal form. Player one's choices are shown on the left vertical axis, and player two's choices are shown on the top horizontal axis. The payoffs for each player are in their corresponding intersections and are displayed as follows (player one, player two).

Important

Game theory surmises that one player's payoff is contingent on the strategy implemented by the other player. 

The Nash Equilibrium

Nash Equilibrium is an outcome reached that, once achieved, means no player can increase payoff by changing decisions unilaterally. It can also be thought of as "no regrets" in the sense that once a decision is made, the player will have no regrets concerning decisions considering the consequences.

The Nash Equilibrium is reached over time in most cases. However, once the Nash Equilibrium is reached, it will not be deviated from. After learning how to find the Nash Equilibrium, individuals can take a look at how a unilateral move would affect the situation. Does it make any sense? It shouldn't, and that's why the Nash Equilibrium is described as "no regrets."

Finding Nash Equilibria

Step One: Determine player one's best response to player two's actions.
When examining the choices that may maximize a player's payout, how does player one respond to each of the options player two has? An easy way to do this visually is to cover up the choices of player two. Consider the example matrix:

Player one / Player two Left Right
Up (1, -) (4, -)
Down (3, -) (3, -)

Player one has two possible choices to play: "up" or "down." Player two also has two choices to play: "left" or "right." In this step of determining Nash Equilibrium, look at responses to player two's actions. If player two chooses to play "left," we can play "up" with a payoff of 1 or play "down" with a payoff of 3. Since 3 is greater than 1, we will bold the 3, indicating the option to play "down."

If player two chooses to play "right," we can either choose to play "up" for a payoff of 4 or play "down" for a payoff of 3. Since 4 is greater than 3, we bold the 4 to indicate the option to play "up." The bold outcomes are shown below on the full matrix.

Player one / Player two Left Right
Up (1, 3) (4, 2)
Down (3, 2) (3, 1)

Step Two: Determine player two's best response to player one's actions.
As we did before with the player two payoffs for player one, we will hide the payoffs of player one when determining the best respo⭕nses for player two.

Player one / Player two Left Right
Up (-, 3) (-, 2)
Down (-, 2) (-, 1)

Just as when looking at player one, each player has two choices to play. If player one chooses to play "up," we can play "left," with a payoff of 3, or "right," with a payoff of 2. Since 3 is greater than 2, we bold the 3 to show the option to play "left." If player one chooses to play "down," we can play "left" for a payoff of 2 or "right" for a payoff of 1. Since 2 is greater than 1, we bold the 2, indicating the option to play "left." The bold outcomes are shown below on the full matrix.

Player one / Player two Left Right
Up (1, 3) (4, 2)
Down (3, 2) (3, 1)

Step Three: Determine which outcomes have both payoffs in bold. That particular outcome is the Nash Equilibrium.
Now, we combine the bold options for both players onto the full matrix.

Player one / Player two Left Right
Up (1, 3) (4, 2)
Down (3, 2) (3, 1)

Look for intersections where both payoffs are bold. In this case, we find the intersection of (Down, Left) with the payoff of (3, 2) fits our criteria. This indicates our Nash Equilibrium.

This method of finding Nash Equilibrium is well-suited to finding equilibria in games that are🥃 simultaneous since ꧅we are looking at how a player would respond independently of how the other acts.

Airline Pricing Example

This scenario of a simultaneous game is often played out in businesses such as airlines. Below is an example, similar to the game above, of how airline pricing may play out. The payouts are in thousand෴s of dollars. Remember, these are the payouts, not the prices. The method we applied previously is already appli💟ed to show where the Nash Equilibrium appears.

Airline one / Airline two Low Price High Price
Low Price (3,000, 3,000) (4,000, 2,000)
High Price (2,000, 4,000) (3,500, 3,500)

Looking at A1's choices we see that if A2 chooses to play low price, we choose between low price for 3,000 or high price for 2,000. We choose low since 3,000 > 2,000. We do the same thing for A2 playing high price and see that we play low because 4,000 > 3,500.

Conversely, looking at A2's choices, we can see that if A1 chooses to play low price, we choose between "low price" for 3,000 and "high price" for 2,000. Since 3,000 > 2,000, we choose the "low" price option here. If A1 plays a "high" price, we can charge a low price of 4,000 or a high price of 3,500. Since 4,000 > 3,500, we choose to play low price here.

The Nash Equilibrium is that both airlines will charge a low price (shown when choices for each party are highlighted). If both airlines charged a high price, theওy would each be better off than they are at𓃲 the Nash Equilibrium.

So why don't they agree to do this? It's illegal to collude. If this were to occur, a unilateral action on behalf of one airline to charge a low price would be beneficial, resulting in that airline making ✤more money in turn. This logic also shows how the Nash Equilibrium is reached and why it is not beneficial to deviate ཧfrom it once it is reached.

Who Developed the Nash Equilibrium?

Nash equilibrium is named after 澳洲幸运5官方开奖结果体彩网:John Nash, an American mathematician.

Can There Be Multiple Nash Equilibria?

There can be more than one equilibrium in a game. However, this usually occurs in games with more complex elements than two choices by two players. In simultaneous games that are repeated over time, one of these multiple equilibria is reached after some trial and error. This scenario of differing choices over time before reaching equilibrium is the most often played out in the business world when two firms are determining prices for highly 澳洲幸运5官方开奖结果体彩网:interchangeable products, such as airfare or soft drinks.

How Does Game Theory Help Find the Best Payoff?

Using Nash equilibrium helps a player 澳洲幸运5官方开奖结果体彩网:determine the🌳 best payoff in a situation based on not oꦉnly their decisions but also the decisions of other parties involved.

The Bottom Line

With these advanced methods, more real-world situations can be modeled and solved. The various Nash Equilibria are the most commonly found solutions to real-world modeled games. A working knowledge of game theory can help individuals and companies form a strategy, whether pl🐭aying tic-tac-toe or vying for the largest profits.

Article Sources
Investopedia requires writers to use primary sources to support their work. These include white papers, government data, original reporting, and interviews with industry experts. We also reference original research from other reputable publishers where appropriate. You can learn more about the standards we follow in producing accurate, unbiased content in our editorial policy.
  1. Holt, Charles A. and Alvin E. Roth. "." PNAS, vol. 101, no. 12, March 2004, pp. 3999-4002.

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