How do TV networks know how many viewers are watching a show?
Wikipedia has a good reference on the Nielsen ratings, including a number of useful digressions. I’ll try to summarize: Nielsen’s ratings calculation, also called Cume Rating (or “Reach”), measures the number of unique viewers or households tuned to a television program in a particular time period during a week. The Cume itself is calculated by dividing the number of unique viewers or households by the total number of estimated available households/viewers/listeners possible. This gives a percentage Cume rating. • Viewers in various demographics are given diaries or set top boxes. Both are for recording what the household’s viewers are watching at any given time. Of course the diaries are subject to the keeper’s own accuracy and honesty. They can also account for the use of DVRs. • Ratings points represent the number of households as a percentage of all television households. Share represents the
