Abstract: Among other things, participants who belong to a crowd of participants can provide indications of relative values of ideas that belong to a body of ideas. A rank ordering according to the relative values of at least some of the ideas of the body is derived based on the indications provided by the participants. The participants can provide the indications in two or more rounds. Each of at least some of the participants provide the indications with respect to fewer than all of the ideas in the body in each of the rounds. Between each of at least one pair of successive rounds, the set of ideas is updated to reduce the role of some of the ideas in the next round.