National ratings of the popularity of U.S. television shows.
Developed by A.C. Nielsen in 1950, the system now samples television viewing in about 5,000 homes. A meter attached to each television set records the channel being watched and sends the data to a computer centre; individual buttons record which person in each household is watching a given program. Separate surveys are done for many large media market areas. The ratings project each program's total audience; for example, a rating of 20 denotes that 20% of U.S. households tuned in to a particular program. Commercial television networks use the ratings to set advertising rates for each program as well as to determine which programs to continue and to cancel.