More Effective Choice in the Prisoner's Dilemma

TLDR

The study analyzes the second round of the iterated Prisoner’s Dilemma computer tournament to deepen understanding of effective strategies. Entrants incorporated lessons from the first round into their designs, and robustness was confirmed by analyzing hypothetical alternative tournaments. TIT FOR TAT emerged as the winner, illustrating that avoiding early defection, exercising forgiveness, and allowing provocation are key to success while highlighting subtle pitfalls for certain decision rules.

Abstract

This study reports and analyzes the results of the second round of the computer tournament for the iterated Prisoner's Dilemma. The object is to gain a deeper understanding of how to perform well in such a setting. The 62 entrants were able to draw lessons from the results of the first round and were able to design their entries to take these lessons into account. The results of the second round demonstrate a number of subtle pitfalls which specific types of decision rules can encounter. The winning rule was once again TIT FOR TAT, the rule which cooperates on the first move and then does what the other player did on the previous move. The analysis of the results shows the value of not being the first to defect, of being somewhat forgiving, but also the importance of being provocable. An analysis of hypothetical alternative tournaments demonstrates the robustness of the results.