Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for evaluating the impact of events related to user interfaces on target outcomes. In one aspect, a method includes defining a set of sequential events including a target outcome and a series of lead-up events that are required to occur prior to the target outcome. The processor(s) identify matching sessions during which at least one of the lead-up events was performed based on session data for each matching session including data identifying the at least one lead-up event. The processor(s) examine session data for each of the matching sessions to determine how many of the matching sessions included a specified session feature. The impact of the specified session feature on the target outcome is determined based on an unrealized metric of the matching sessions that included the specified session feature, but did not include the target outcome.