Tit For Tat - Example of Play

Example of Play

Assume there are four agents: two use the tit-for-tat strategy, and two are "defectors" who will simply try to maximize their own winnings by always giving evidence against the other. Assume that each player faces the other three over a series of six games. If one player gives evidence against a player who does not, the former gains 5 points and the latter nets 0. If both refrain from giving evidence, both gain 3 points. If both give evidence against each other, both gain 1 point.

When a tit-for-tat agent faces off against a defector, the former refrains from giving evidence in the first game while the defector does the opposite, gaining the control 5 points. In the remaining 5 games, both players give evidence against each other, netting 1 point each game. The defector scores a total of 10, and the tit-for-tat agent scores 5.

When the tit-for-tat agents face off against each other, each refrains from giving evidence in all six games. Both agents win 3 points per game, for a total of 18 points each.

When the defectors face off, each gives evidence against the other in all six games. Both defectors win 1 point per game, for a total of 6 points each.

Each tit-for-tat agent scores a total of 28 points (18 against the fellow tit-for-tat, 5 against each of the two defectors), over the eighteen matches. Each defector scores only 26 points (6 against the fellow defector, 10 against each of the tit-for-tats).

Despite the fact that the tit-for-tat agents never won a match and the defectors never lost a match, the tit-for-tat strategy still came out ahead, because the final score is not determined by the number of match wins, but the total points score. Simply put, the tit-for-tat agents gained more points tying with each other than they lost to the defectors.

The more tit-for-tat agents that there are in the described game, the more advantageous it is to use the tit-for-tat strategy. The fewer tit-for-tat agents that there are in the described game, the less advantageous it is to use the tit-for-tat strategy.