What controls network reciprocity in the Prisoner's Dilemma game?

The evolutionary Prisoner's Dilemma game in structured networks has been studied extensively to understand network reciprocity. However, in some cases results of these studies cannot be compared because not only the network structures but also the network parameters, rules for updating strategies, and update dynamics differ among them. In this study, we investigated the effect of experimental conditions by conducting a series of systematic factorial experiments. We found that those experimental assumptions are significantly important in network reciprocity, although we confirmed that network reciprocity can be basically explained by the average degree of the network (Nowak, 2006; Ohtsuki et al., 2006).