Game Theory II: Axelrod's Tournaments - Vocabulary

Vocabulary flashcards covering payoffs, strategies, and findings from Axelrod's Tournaments in Game Theory II.

Prisoner's Dilemma

A two-player game where each can choose to Cooperate or Defect; payoffs follow T > R > P > S, with looping repeats allowing strategies to condition on past moves.

Temptation to Exploit (T)

Payoff for defecting when the other player cooperates (in the notes, T = 5).

Reward for Mutual Cooperation (R)

Payoff when both players cooperate (R = 3 in the notes).

Punishment for Mutual Defection (P)

Payoff when both players defect (P = 1 in the notes).

Sucker's Payout (S)

Payoff for cooperating when the other defects (S = 0 in the notes).

Sustained Cooperation

Long-run mutual cooperation yields higher payoffs than alternating exploitation; considered crucial in repeated PD. 'CRUCIAL: sustained cooperation > taking turns exploiting.'

Axelrod's Tournament

A competition where strategies play many rounds of the Prisoner’s Dilemma to identify robust strategies; includes self-play and multiple opponents over 200 rounds; winners are those with the highest final score.

Nice Strategy

A strategy that tends to cooperate (is not immediately exploitative) and often starts with cooperation.

ALL C

Always Cooperate; a strategy that cooperates every round regardless of the opponent.

ALL D

Always Defect; a strategy that defects every round regardless of the opponent.

RANDOM

A strategy that assigns a 50/50 chance of defecting or cooperating each round.

DOWNING

Defects on unresponsive players; starts with a double defection.

FRIEDMAN

Starts by cooperating; if ever defected on, defects back forever.

TIT FOR TAT

Cooperate on the first move and then copy the opponent’s previous move.

JOSS

TIT FOR TAT variant with a 10% chance of defecting on a cooperator.

TIT FOR TWO TATS

Like TIT FOR TAT but defects back only after two defections by the opponent.

Best Response to ALL C

All D (defect) is the best reply to an all-cooperator opponent.

Best Response to ALL D

All D (defect) is the best reply to an all-defector opponent.

Best Response to RANDOM

All D (defect) is the best reply to a random opponent.

Self-Play

In Axelrod’s first tournament, strategies faced themselves as opponents.

200-Round PD

Each match in the tournament consists of 200 rounds of Prisoner’s Dilemma.

No Dominant Strategy

There is no single strategy that is best against all possible opponents.

Robust Strategy

A strategy that performs well across a variety of opponents; the goal of Axelrod’s tournaments.

Niceness and Forgiveness

Traits that contributed to TIT FOR TAT’s success: cooperates (niceness) and forgives occasional defections.