Decision, Vol 12(2), Apr 2025, 111-145; doi:10.1037/dec0000259
Prisoner’s dilemma (PD) games exist in a variety of configurations. Although the normative solution for any one-shot PD game is defection, empirical research shows that games differ in the amount of cooperation they elicit from human players. Different researchers have developed a variety of indexes, which are functions of the specific payoffs in a given PD, aiming to measure the level of anticipated cooperation elicited by that game. The purpose of the first study in this article was to collect, organize, and compare the mathematical properties of these various indexes. Our results show that many superficially different indexes are the same and that in general six fundamental PD indexes exist. We propose that the six families of indexes correspond to psychological processes and preferences involving prosociality, greed, fear, and risk. In the second study, we provide a meta-analysis of the relationship between selected indexes and cooperation in PD games (k = 280). The amount of variance in cooperation explained by each index ranged from 0.00% to 7.57%. The first family of indexes (described as indexes of the incentive for cooperation in the first study) had the most consistently strong relationships with cooperation. In general, the findings of the meta-analysis aligned with predictions based on our own review and taxonomy of six index families proposed in Study 1. (PsycInfo Database Record (c) 2025 APA, all rights reserved)