22. The method according to claim 20 wherein said cut-off point is selected from all ranks of documents in said control subset so as to maximize a quality criterion.
22. The method according to claim 20 wherein said cut-off point is selected from all ranks of documents in said control subset so as to maximize a quality criterion. 24. The method according to claim 22 wherein said at least one quality criterion characterizing said binarizing of said rankings of said documents in said control subset comprises at least one of the following criteria: an F-measure; a precision parameter, and a recall parameter.