29. The system of claim 27 , wherein the ranking calculator is configured to calculate the ranking values for the two or more contributors in an iterative process comprising repeated calculation of interim ranking values for the two or more contributors.
30. The system of claim 29 , wherein the ranking calculator is configured to calculate the interim ranking values in an iterative process that comprises calculating the interim ranking values in a calculation sequence, the system further comprising a sequencing module to determine the calculation sequence based at least in part on respective initial ranking values, with lower initial ranking values being earlier in the calculation sequence.