Conversion path performance measures and reports

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for providing content performance measures and reports. In one aspect, a method receives a request for a user interaction report that specifies measures of user interactions with content items for a reporting period. Initial user interaction data representing user interactions with content items over the reporting period are obtained, where the user interaction data is associated with unique identifiers that each represent a user device with which user interactions are associated. For each of the unique identifiers an initialization time that specifies a time at which the unique identifier was associated with a user device is determined. In turn, initial user interaction data that are associated with unique identifiers having at least a minimum age are selected as final user interaction data, where the age of a unique identifier is an amount of time between the initialization time for the unique identifier and a time at which the conversion occurred. The user interaction report is generated using the final user interaction data.