The four radio companies represent a broad swath of radio airplay in the United States. Premiere Radio Networks, a subsidiary of Clear Channel, syndicates 90 radio programs to 4,600 affiliate stations. Westwood One, managed by CBS Radio, syndicates 150 programs to 5,000 stations around the country. Jones Media America syndicates 120 programs and services, and Dial Global is the country's largest independent network, representing 60 independent producers and syndicators.
The participating radio companies must encode their advertising for measurement by Arbitron's Portable People Meter as part of the Apollo Project. The Apollo Project is a joint venture between Arbitron and the Nielsen Company that seeks to achieve holistic measurement of all media exposure, including TV, radio, magazines, newspapers and Internet, then correlate it with actual purchasing patterns. It relies on a panel of over 11,000 individuals in 5,000 households in the Houston area. Arbitron's PPM handles measurement of exposure to various electronic media including radio and TV. Purchase tracking is performed by AC Nielsen Homescan