How does it work? According to Arbitron's website:
"The Arbitron Portable People Meter technology tracks consumers' exposure to media and entertainment, including broadcast, cable and satellite television; terrestrial, satellite and online radio as well as cinema advertising and many types of place-based digital media.
Broadcast signals are encoded with inaudible signals as they air or stream live. These codes are detected by the software that can be downloaded into a cell phone device or computer application. The PPM software is equipped with a motion sensor, a patented quality control feature unique to the system, which allows Arbitron to confirm the compliance of the PPM survey participants every day."
Arbitron contacts individuals (called panelists) in markets where listener surveys are to be conducted. The company builds a random sample by assembling the panelists which eventually become a "panel" - a group of people who have agreed to carry the PPM. (In Arbitron's original diary method, the "panel" was called the "sample".)
PPM survey periods last for 28 days.
After the data is compiled, Arbitron reports three basic audience estimates:
Persons: the estimated number of persons listening
Rating: the percent of the survey area population listening to a station
Share: the percent of all radio listening that occurs with a particular station.
The latest generation of PPM technology is the PPM 360. Arbitron says:
The new device design resembles a simple cell phone and is sleeker and smaller than the current meter. The inclusion of cellular wireless technology in the meter eliminates the need for an in-home docking station and a communications hub, creating an enhanced, streamlined experience for a panelist."