Picking the winners

We analyze the problem of choosing the w contestants who will win a competition within a group of n > w competitors when all jurors commonly observe who the w best contestants are, but they may be biased. We study conditions on the configuration of the jury so that it is possible to induce the jurors to always choose the best contestants, whoever they are. If the equilibrium concept is dominant strategies, the condition is very strong: there must be at least one juror who is totally impartial, and the planner must have some information about who this juror is. If the equilibrium concept is Nash (or subgame perfect) equilibria the condition is less demanding: for each pair of contestants, the planner must know that there is a number of jurors who are not biased in favor/against any of them and he must have some information about who these jurors are. Furthermore, the latter condition is also necessary for any other equilibrium concept.