12. The method of claim 11 , wherein the updating comprises: for each of a subset of the other users whose user profiles include a pairwise ranking for a selected pair of the machine translation systems, computing a similarity between the first user's user profile and the respective other user's user profile; identifying, based on the computed similarities, a set of the other users as nearest neighbors to the first user; computing a pairwise ranking for the pair of the machine translation systems as a function of the pairwise rankings of the nearest neighbors for the selected pair of machine translation systems.
14. The method of claim 12 , wherein the identifying of the set of the other users as nearest neighbors to the first user comprises applying at least one criterion for inclusion of the other users in the nearest neighbors.