Radio ratings measure the number of individual persons in the audience for each radio station. Since the 1950s, radio has become largely a local medium. That is, most radio programming does not originate at the network level. Local broadcasters assemble music, news, talk, and other forms of entertainment at a single local studio and transmit them to a local audience. National radio ratings do exist, but are insignificant to a basic understanding of radio ratings.
Radio is essentially a local phenomenon in America.
Arbitron specializes in local radio ratings, as does Birch Radio. Weekends have unique dayparts of their own. The CUME statistic measures the number of individual persons who tune into a given radio station in a calendar week. For each quarter- hour, within every hour of every day, an audience sample is taken. Listeners are counted for any and every quarter-hour in which they participate.