1. A method implemented in a computing device, the method comprising: storing, in the computing device, a set of cell identifiers for a plurality of geographical regions each having predefined geographical boundaries, each of the cell identifiers identifying a cell that is determined to be within a region defined by one of the predefined geographical boundaries and stored in association with the region; receiving coordinates of locations of a plurality of mobile devices as a function of time; computing, by the computing device, visitation data representing visitations of the mobile devices to the geographical regions as a function of time by: converting the coordinates of the locations of the mobile devices into respective cell identifiers; and searching, in the set of cell identifiers, the respective cell identifiers to determine respective geographical regions that contain the locations of the mobile devices corresponding to the respective cell identifiers; receiving, by the computing device from a separate device, a set of mobile device identifiers; retrieving, by the computing device and from the visitation data of the plurality of mobile devices, visitation data of selected mobile devices that are identified by the set of mobile device identifiers; transmitting, by the computing device to the separate device, a first data set associating the visitation data of the selected mobile devices with respective mobile device identifiers of the selected mobile devices, the transmitting of the first data set causing the separate device to generate a second data set by: associating status data of the selected mobile devices with the visitation data of the selected mobile devices; and disassociating the mobile device identifiers of the selected mobile devices from the status data provided in the second data; receiving, by the computing device from the separate device, the second data set containing the status data of the selected mobile devices and the visitation data of the mobile devices but having no indication of respective association between the mobile device identifiers of the selected mobile devices and the status data of the selected mobile devices; identifying, by the computing device from the second data set: visitation data of a first subset of the selected mobile devices having a first status identified by the status data; and visitation data of a second subset of the selected mobile devices having a second status identified by the status data, wherein the first and second subsets of mobile devices have matching patterns of visitation to the geographical regions prior to a time period; and measuring, by the computing device, a difference, between the first subset of the selected mobile devices and the second subset of the selected mobile devices, in visitation patterns to the geographical regions after the time period.