Bidding Strategy (English Auctions)
A strategy is a description of how the bidder will behave in every possible situation.
Best Response
Suppose there are
- The outcome of the auction when everyone uses that strategy can be computed.
- We can call the outcome
- We can call the outcome
- Your strategy
is a best response to if there is no such that is better for you than .
This model doesn’t account for people who change their strategies.
If
Rationalisability
A strategy
- There are strategies
that is best response to. are rationalisable.
Therefore, everyone is playing the best response at least one other person’s strategy, given that everyone is playing a rationalisable strategy.
Not every rationalisable strategy is optimal.
Optimality
A strategy
- If an optimal strategy exists you should use it.
- Otherwise default to a rationalisable one.
Every optimal strategy is rationalisable.
English Auction Strategy
Consider we are in an English auction with the following assumptions:
- There are exactly two bidders.
- The minimum increase is negligible.
-
The item is worth
to you.You should not bid more than
otherwise you will be disappointed.
- Suppose that the current standing bid
by the other bidder and . -
Raise with the following inequality:
where
is your new bid.
You can never be certain what your opponent will do. Therefore you must follow these rules as you can’t be sure whether you will be outbid or not.
English Auctions with Minimum Increase
You can make use of the minimum raise to increase your profit:
- Consider that you know your competitor values the item at £100 and you at £150. There is a minimum raise of £10.
- If you are able to bit £91 then the other bidder can no longer raise. Therefore you have a profit of £150 - £91 = £59.
Before we would have only gained a profit of £40. By getting the bid right we can increase profit by up to twice the minimum raise.
If your information is false then you can end up making a reduced profit by raising too quickly.