What is the difference between Diary and Portable People Meter (PPM) measurement methods?

The key difference between Diary and Portable People Meter (PPM) measurement methods lies in how audience listening habits are captured. The Diary method involves a representative panel of participants who manually record their radio listening habits in a paper diary provided by Arbitron. Participants jot down the station and time they listen. On the other hand, the PPM method utilizes a small, portable device that participants carry throughout their day. The device automatically detects and records inaudible codes embedded in audio broadcasts. These codes are then sent wirelessly to Arbitron for analysis. The PPM offers a more accurate and detailed measurement of listening habits as it overcomes the limitations of human error and recall in the Diary method. It provides real-time data and captures a broader range of listening, including out-of-home and digital media sources, while the Diary method mainly focuses on in-home listening.