A system and method are disclosed for automatically detecting associations between particular sets of search criteria, such as particular search strings, and particular items. Actions of users of an interactive system, such as a web site, are monitored over time to generate event histories reflective of searches, item selection actions, and possibly other types of user actions. An analysis component collectively analyzes the event histories to automatically identify and quantify associations between specific search strings (or other types of search criteria) and specific items. As part of this process, a decay function reduces the weight given to a post-search item selection event based on intervening events that occur between the search event and the item selection event.