1. A computer-implemented method comprising: receiving 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 production scoring function; processing the set of item listings with a test scoring function to assign to each item listing in the set of item listings a position at which each item listing would appear if presented in a second search results page; based on the position at which the converting item listing would appear if presented 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 test scoring function; with the number and direction of positions that the particular item listing has shifted, deriving an average rank shift for the test scoring function, the average rank shift representing an average number and direction of positions that a converting item listing is shifted as a result of processing a predetermined number of sets of item listings with the test scoring function; and displaying the average rank shift.