It is not possible to sign up to participate in any Nielsen studies, as of 2015. All participants are randomly selected and every family in the United States has an equal chance of being selected. Nielsen may contact potential panelists by phone or mail.
Nielsen Media Research uses statistical sampling to create its television ratings, which is the same technique used to predict the outcome of elections. The company creates a sample population from which to gather data and then extrapolates from that data to estimate the viewing habits of the nation.
Nielsen asks around 5,000 households to be a part of its representative sample. Since the company estimates there are 99 million households in the United States with a television, this is a very small sample, making it very important that the sample is representative. This means the demographics of the sample need to closely match the demographics of the entire nation.
To monitor viewing habits, Nielsen installs TV meters in the selected households. This meter tracks when the TV is turned on and to what channel it is tuned. The information gathered by the meter is sent to Nielsen each night.
The TV ratings created by Nielsen are worth billions of dollars, as of 2015. Advertisers select which shows and what times to air their commercials based on the research done by the company. Programmers also use the data to decide which shows to keep and which to cancel.