1. A computer-implemented method comprising: receiving, from a listing data structure, a set of item listings satisfying a search query and a slot listing number identifying the position of a particular item listing that has resulted in a conversion of an item, the set of item listings having been presented in a first search results page with each item listing positioned in an order determined by processing the set of item listings with a processor-implemented production scoring function; processing the set of item listings with a processor-implemented test scoring function to assign to each item listing in the set of item listings a position for presenting the item listing in a second search results page; based on the position for presenting the item listing in the second search results page, determining a number and direction of positions that the particular item listing has shifted from its position in the first search results page as a result of the set of item listings being processed with the processor-implemented test scoring function; with the number and direction of positions that the particular item listing has shifted, deriving, using a rank shift module, an average rank shift for the processor-implemented test scoring function, the average rank shift representing an average number of positions that a set of item listings that have resulted in conversion of items have shifted as a result of processing a predetermined number of sets of item listings with the processor-implemented test scoring function, each set of item listings of the predetermined number of sets of item listings corresponding to a different query; and displaying the average rank shift for the processor-implemented test scoring function.