Marketing by the numbers
Nielsen ratings are very important to both advertisers and television programmers because the cost of television advertising time holds in Nielsen’s sample tuned to that program divided by the number of television-owning households-11.5 million in the United States. A show’s share of the viewing audience is the number of households, whereas share watching that show divided by the number of households using TV at that time. That is, ratings consider all TV-households, whereas share considers only those households that actually have the television on at the time. Rating and share are usually given together. For example during one evening hour on September *, 2010, the following ratings/shares were reported for the major broadcast net works: