Transcript The Stag Hunt Game - University of Birmingham

The Stag Hunt Game
Introduction
The stag hunt, first proposed by Rousseau, is a game which
describes a conflict between safety and social cooperation.
The concept goes something like this:
Two hunters go out for the day looking for some prey. There are
three possible targets...a large stag and a couple of hares. The
only way to get a stag is for both hunters to work together.
However if one goes for the stag and the other goes for a hare;
he’ll end up with nothing. If you’re hunting for hares by yourself,
you will get two for sure. If both hunters go for hares, each will
get one; and therefore will have dinner regardless of what the
other has chosen.
Therefore although hunting a hare produces less meat, it is potentially
advantageous because it is really easy.
Assumptions of the Model
• There is no communication between the two
hunters.
• The Stag yields more food than the Hare.
• In any given scenario, at least one hunter is
guaranteed food.
• Both hunters are rational and equally
informed.
• The numbers on the matrices represent the
utiles gained from payoffs.
Risk Dominant and Pay-off
Dominant Equilibrium
•A game is said to be in Nash equilibrium when
no player has incentive to change their strategy
given the strategies of all other players that are
•Pay-off Dominant equilibrium = Stag, Stag
strategy pair
•Risk-Dominant equilibrium= Hare, Hare.
Strategy pair
•The Strategy pair Stag, Stag gives a higher pay
off than Hare, Hare. However the strategy pair
Hare, Hare provides less risk due to uncertainty
of each hunters actions. The strategy pair Hare,
Hare provides a higher expected pay-off.
Hunter 1
Hare Stag
playing.
Hunter 2
Stag
80,80
N.E
Hare
10,50
50,10
50,50
N.E
Main Paper
• Loss Avoidance as Selection Principle: Evidence from Simple StagHunt Games: Ondřej Rydval, Andreas Ortmann
 This paper investigates the conjecture that loss avoidance solves the tension
in stag-hunt games for which payoff dominance and risk dominance make
conflicting predictions.
 We look at affine transformations of the stag hunt game and see how it affects
human behavior. The risks don’t change in any of the games.
 We are primarily concerned with whether potential losses will make people
more likely to coordinate (pay-off dominant), contrary to textbook wisdom.
Game 2
-60
B A
B A
Game 1
Secondary Papers
• The Stag Hunt by Brian Skyrms and U. C. Irvine. This
paper gives a good overview of the Stag Hunt game
along with the introduction of new variables and
changes assumptions such as the probability of success
of each individual hunt.
• Optimization Incentives And Coordination Failure
In Laboratory Stag Hunt Games by Raymond
Battalio, Larry Samuelson, and John Van Huyck. This
paper conducts three stag hunt games in which the risk
dominant and the payoff dominant solutions conflict.
This leads to an inefficient pure strategy outcome.
• These papers will be used in conjunction with the main
paper in our final presentation.
Questions that will be
answered:
• Will loss avoidance change the
incentives of the players towards a
payoff dominant equilibrium?
• By changing some of the
assumptions, how does this affect
the model.
• How does this model represent
certain aspects of the economic
world.
Thank you for listening