Television ratings are measurements that indicate how many viewers are watching a particular program. These ratings help networks and advertisers understand the popularity of shows and make decisions about scheduling and advertising. Ratings are typically expressed as a percentage of the total number of households with televisions. The most common system for measuring ratings in the United States is conducted by Nielsen Media Research. They use a combination of electronic devices and surveys to gather data on viewing habits. Higher ratings can lead to increased advertising revenue for networks, as more viewers attract more advertisers.