Mailing lists of consumers are generally compiled from a variety of sources. For example, they can be obtained using phone books, city directories, mortgage data, survey data, warranty registrations and various other sources. Many of the sources are then merged together to create the best possible list. Using many of the USPS's tools for updating, such as National Change of Address (NCOA), Delivery Point Validation (DPV) and Coding Accuracy Support System (CASS) certification, helps cleanse the files. Using various other data such as census information, credit reporting, buying habits and psychographics, adds important additional information to better pinpoint those consumers for specific communication or marketing purposes.