Iterative Deletion of Dominated Strategies

As I mentioned before, not all games have a strictly dominant strategy. However, there’s another way we can use the concept of strictly dominated strategies to find equilibria.

Let’s say we have another two-player game. The players have choices A, B, C, and D. Player 1’s payoff is negative one if players play B,D, zero if they play B,C, or A,D, and one if they play A,C. Player 2’s payoffs are five if they play A,C, and two if they play A,D, and… actually there’s no point in me saying what his payoffs are in the other two cases, because we already have enough information to find an equilibrium.

But how can that be? It’s simple. Player 2 knows player 1’s payoffs, and he knows that player 1 is rational. So he knows that player 1 will not play B, because player 1 is always better off playing A. B is strictly dominated by A, so player 2 can ignore the possibility that B will be played. So we can delete B as an option, and then we see that player 2 must choose C, as A,C gives him a larger payoff than does A,D.

This might be an dominant strategy equilibrium depending on player 2’s payoffs, but it doesn’t have to be.

Here’s a more complicated example. There’s no dominant strategy equilibrium here, but let’s see if we can find an equilibrium by deleting the strictly dominated strategies.

We can see that player 1 will never pick C because he’s always better off choosing B, so let’s delete that. Now, given that C has been deleted, F can be deleted also. A,F and B,F both give player 2 a payoff of zero, and he could get a payoff of one by playing G, so he won’t play F. With F deleted, player 1 won’t ever play A, since he can always be better off playing B. That leaves player 1 playing B for sure, and player 2 can clearly see that he get his highest payoff in B,D, so he can eliminate E and G.

So there you have it, an equilibrium.


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All Comments

  • GREAT GREAT WORK! Beautiful explanation!

    Sreetama Ray July 13, 2020 8:24 pm Reply
  • I’m confused at the key he’s using. What do all those values indicate?

    Siddharth Venkat July 13, 2020 8:24 pm Reply
  • Good video, using bigger matrix is a good visualization

    Guhan Thuran July 13, 2020 8:24 pm Reply
  • Nice 🙂 thank u.

    Rahul Sinha July 13, 2020 8:24 pm Reply
  • Thank you !!!! :')

    Brising Conan July 13, 2020 8:24 pm Reply
  • matematica di tipo elliederico

    RTF HERRD July 13, 2020 8:24 pm Reply
  • thanks!

    Tsunayoshi Sawada July 13, 2020 8:24 pm Reply
  • Must the elimination always be alternating? like player 1 then player 2 then player 1….or can it be player 1 player1 player2 player 2?

    joesr31 July 13, 2020 8:24 pm Reply
  • so is D the best choice for P2? I'm a bit confused.

    Caeser Tullo July 13, 2020 8:24 pm Reply
  • Writing a paper in school about the Game Theory in general, would really like to get some explanation for the Bayesian Equilibrium and the Weak Perfect Bayesian Equilibrium. mind uploading a video for those?

    Scrotch N soda July 13, 2020 8:24 pm Reply
  • Why F can be deleted? Please explain.

    Shahrear Towhid July 13, 2020 8:24 pm Reply
  • Sick

    jhewitt2008 July 13, 2020 8:24 pm Reply
  • I like this approach 🙂

    Manasi Chhabra July 13, 2020 8:24 pm Reply
  • great videos, keep em coming!

    WeNeedCarlSaganBack July 13, 2020 8:24 pm Reply

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