MobLab
Guides
Aa

Private Value English Auction

Game Description

Each bidder has a randomly determined private value for one unit of a good. Participants see the bids of others, and bids can be made until the end of the auction, as long as it is higher than the current highest bid. The highest bidder when time expires is the winner.

Learning Objective 1: Private-Value English Auction

Demonstrates the workings of a private-value English auction.

Learning Objective 2: Equilibrium Bidding Strategy

A player’s equilibrium bidding strategy is to bid as long as the current price is less than or equal to her value of the item after her bid.

Learning Objective 3: Relation to Other Types of Auctions

Play this game in conjunction with the first price private-value sealed bid auction (or the descending clock auction) to show the difference in optimal bidding strategy. You can also show that the optimal bidding strategy in the private-value English auction is equivalent to that of the second price private-value sealed bid auction (or the ascending clock auction).

Brief Instructions

Each bidder values one unit, and this value is by default drawn from the uniform distribution with Lowest Bidder Value=$10 to Highest Bidder Value=$100. Each bidder draws a new value for each new period if multiple rounds are specified (Periods > 1).

Each player has a weakly dominant strategy to bid up to her value. When the Current Price is greater than or equal to Buyer Value, the bidder should stop bidding.

Note: In order to increase the likelihood that a player can bid up to her value, make sure Price Increment= 1.

Results

The results highlight the Nash Equilibrium and show how close your students were to equilibrium play. Use the Go To: menu to switch between periods.

Figure 1: Outcome Summary Table

For each round, there is a table summarizing each group’s performance (Figure 1). The first columns display the highest item value (Optimal Surplus) and the winner's item value (Surplus).1 The final column shows seller Revenue (the winning bid). Check the radio button to reveal a figure summarizing a group’s bidding.

Figure 2: Participant Bids and Values

By unchecking the check-box for the Nash Equilibrium Bid Function, only markers that indicate bidder value and the final (highest) bid for each participant remain (Figure 2). The winning bidder is assigned a different marker from other bidders.

Figure 3: Nash Equilibrium Bid Function

The equilibrium strategy in this auction is such that a player's highest bid does not exceed her value. A graph consistent with Nash bidding satisfies two conditions: 1) no bids above the Nash Equilibrium Bid Function, and 2) the winning bid belongs to the bidder with the highest value (i.e., the rightmost value in the graph.)

Robot Play

Our robot (i.e., an automated player) strategy is the following:

If the current high bid is lower than their value, the robot will increase the bid to a random number between the highest bid and a number halfway between their value and the highest bid.

Example

If the current bid is $50 and the robot's value is $70, the robot will raise the bid to a random number between $51 and $60.

1. Surplus calculations assume the items have no value to the seller.
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