Television programming is big business, with sales of interstitial advertising reaching billions of dollars annually. Advertising rates are determined by the viewership of the program in question, which has traditionally been determined by ACNielsen, part of The Nielsen Company. Nielsen wields an immoderate amount of industry clout considering its questionable methods of statistics gathering. The Nielsen Company relies on selected households to catalog their television watching habits in "diaries." The ratings are then reported as a percentage that indicates the number of viewers watching a television program at a given time. The company has come under criticism for choosing residences that underreport daytime and late-night television viewing and for over-representing minorities in sample populations. Critics also point to the nonviable practice of measuring how many individuals are watching a given television set and of gauging how attentive the audience is to a program or its advertising.