A computer-implemented policy evaluation system for identifying an optimal combination of operational policies for implementation by a plurality of actors, each actor being capable of adopting any of a plurality of operational policies, the policy evaluation system being configured to iteratively perform the following steps: (i) selecting a first combination of operational policies, the first combination defining a policy for each actor; (ii) receiving vectors of values, each representing the benefit of a respective second combination where all but one of the actors adopts the policy defined for it in the first combination and that actor adopts a different policy; and (iii) estimating a ranking of combinations of policies for the actors in dependence on those values and a previously estimated ranking of combinations of policies for the actors.