Radio stations, like all media, need to know how many people are listening and who they are. Without audience measurement, advertisers cannot place media buys, broadcasters cannot evaluate their programming, and regulators cannot assess whether public service requirements are being met. Radio audience measurement is more technically complex than it appears, and the methods used have changed significantly with the shift toward online listening.
Rajar in the UK
Rajar (Radio Joint Audience Research) is the UK’s official radio audience measurement body. It surveys around 105,000 respondents per year using listening diaries — participants record every 15-minute period of radio listening for a week. The results are published quarterly and are the definitive measure of UK radio audiences. Every UK commercial and BBC radio station’s performance is judged against Rajar figures. Rajar also measures streaming and podcast listening through its MIDAS (Measurement of Internet Delivered Audio Services) supplement.
Nielsen in the US
In the US, Nielsen Audio (formerly Arbitron) measures radio audiences using a combination of paper diaries and the PPM — Portable People Meter, a small device worn by panellists that automatically detects inaudible codes embedded in radio station broadcasts. The PPM is more accurate than diaries (which rely on memory) but expensive to deploy. PPM measurement is available in the largest US markets; smaller markets still use diary measurement. Nielsen publishes quarterly book results that drive advertising rates.
Why ratings matter
Radio advertising rates are priced on CPT — cost per thousand — based on the audience a station reaches in a given time slot. A breakfast show with a high weekly reach commands higher rates than a midnight show with a small audience. Programming decisions — whether to change a format, drop a presenter, move a show’s time slot — are made primarily on Rajar or Nielsen data. For commercial stations, audience measurement is the mechanism by which listening translates into revenue.