Fairness In Game Theory

Is it fair to assume that players are entirely self-interested?

People sometimes take others' actions into consideration...

They are kind to those who act kindly towards them

They are hurtful and retaliatory towards those who are unkind

People may not only refuse to help those who are unkind, but will actually sacrifice their payoffs to hurt those who are being unfair.

The Ultimatum Game

The Ultimatum Game is a situation in which a set of individuals must decide upon the division of a fixed sum of money. The game consists of two players, the proposer, who extends an offer to the decider, who can either accept or decline that offer.