Nielsen selects random families be representative populations of the viewing public and then uses proprietary technology to measure their viewing habits. Programs watched in real time and recorded programs watched up to a week after the original airing are included in Nielsen's ratings.
In addition to electronic meters, Nielsen also collects information pertaining to television viewing habits via paper surveys in the midst of sweeps. Sweeps are special periods during the viewing season in which networks amp up their shows in a bid to attract more viewers.
Nielsen acknowledges its greatest challenge is the accurate inclusion of viewing data on the growing list of playback devices. The company attempts to capture and include viewing statistics for mobile devices in its ratings by outsourcing data collection companies to poll television viewers about what they are watching.
In addition to determining how many people watch television programs, Nielsen also breaks the information down into demographic data that provides networks with a view of what percentage of each age group and gender each television program receives. This aids networks in planning television programming for upcoming seasons. Knowing who is watching which programs and when also helps networks determine the most appropriate schedule spot during the viewing week for programs.