1. A method comprising: receiving a sequence of one or more characters entered into a search field on a computing device, wherein the sequence of characters represents a first partial query; providing a first list of query completions for the first partial query for display on the computing device; receiving one or more additional characters entered into the search field upon display of the first list, wherein the sequence of characters and the additional characters cumulatively represent a second partial query; obtaining a second list of query completions for the second partial query; identifying one or more query completions in the second list that appear in the first list; calculating demotion scores for the identified query completions, wherein a demotion score for a particular identified query completion is based at least in part on a weighted value associated with a period of time between when the first list was displayed and when the additional characters were entered, wherein the weighted value is a non-binary measure based on a magnitude of the period of time; using the demotion scores to demote one or more of the identified query completions to a lesser position within the second list, thereby forming a refined second list; and providing the refined second list of query completions for display on the computing device.