Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for detecting and utilizing conversion data are disclosed. In one aspect, a method includes receiving an indication of a user interaction with an advertisement presented at a user device; receiving a user identifier corresponding to the user device; determining that the first application was installed on the user device, based at least in part on a device identifier of the user device being received with installation data corresponding to the installation; receiving, from a second application installed on the user device, (1) the user identifier and (2) the device identifier of the user device; determining, based on receipt of the user identifier and device identifier from the second application that the installation of the first application is attributable to the user interaction.