Fig. 4.

Null hypothesis statistical significance test. Probability of cooperating after playing C or D, conditioned to the context (fraction of cooperative actions in the neighborhood in the previous round), averaged over 10⁶ random shuffling of players. A corresponds to the experimental treatment in the lattice, B corresponds to the same treatment for the heterogeneous network, C corresponds to the control phase in the lattice, and D corresponds to the same control treatment for the heterogeneous network. The results show that there is no dependence on the context and hence, that the results of Fig. 3 A and B are statistically relevant. The anomalous variance (or even absence of data) observed at a fraction of Cs in the neighborhood close to 0.9 is not a relevant feature of the experimental results but a consequence of the very low probability of having events contributing to that bin of the histogram in the heterogeneous network. This anomaly can also be noticed in Fig. 3.