Suppose your favorite television program has just been cancelled because of bad ratings. In the world of television ratings, the number of people watching a show is the important factor, not the intrinsic, qualitative value of the show. So who is rating television shows, and how is it done?

Nielsen Media Research was founded in 1923 to measure the number of people listening to radio programs. Early on, the number of people listening to the radio was low enough to actually count. However, with the advent of television, cable, satellite, and digital television, the number of viewers has greatly increased. In fact, counting the number of viewers of a television show is impossible, so the Nielsen company has devised a way to estimate the number of viewers.

How Ratings Are Determined

Nielsen Media Research measures a sample of television viewers to determine when and what they are...