If any TV network you are watching starts showing Donald Trump live you need to change the channel

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5. That's not how ratings are determined

How do television ratings work?

"In the U.S., the term "TV ratings" immediately makes people think of "Nielsen" because Nielsen Media Research has become the de facto national measurement service for the television industry in the United States and Canada. Nielson measures the number of people watching television shows and makes its data available to the television and cable networks, advertisers and the media.

Nielsen uses a technique called statistical sampling to rate the shows -- the same technique that pollsters use to predict the outcome of elections. Nielsen creates a "sample audience" and then counts how many in that audience view each program. Nielsen then extrapolates from the sample and estimates the number of viewers in the entire population watching the show. That's a simple way of explaining what is a complicated, extensive process. Nielsen relies mainly on information collected from TV set meters that it installs, and then combines this information with huge databases of the programs that appear on each TV station and cable channel.

To find out who is watching TV and what they are watching, the company gets around 5,000 households to agree to be a part of the representative sample for the national ratings estimates. Nielsen's statistics show that 99 million households have TVs in the United States, so Nielsen's sample is not very large. The key, therefore, is to be sure the sample is representative. Then TVs, homes, programs, and people are measured in a variety of ways.
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http://entertainment.howstuffworks.com/question433.htm