Equilibria for a population of DISC players under action implementation error. (a) Cooperativeness (ψ) and (b) ingroup bias (ρ). We fix the number of groups (M = 10) and vary the assignment rule (ST or JG), the probability that a donor fails to help a recipient (ε = 0.01 or 0.1), and the probability of ingroup interaction (θ). The lines represent theoretical results when ε = 0 and are the replicates of those shown in Table 3. The symbols represent numerical results.