Event records can include session data representing a particular consumer and a particular standard period of time, and can include station identification information indicating a media station to which the consumer was tuned during standard period of time. Records can be designated as overlapping event records if multiple event records represent the same consumer and the same period of time, but identify different media stations, and at least some overlapping event records can be eliminated from consideration before determining audience migration information. Audience migration information, including tune-ins and tune-outs, can be determined based on whether or not a consumer has multiple event records showing different media stations at adjacent times. The audience migration information can then be transmitted to an end-user machine for display.