That is an inaccurate interpretation of how the written diary system worked. In fact, a family or person recruited to fill in the diary was only "active" for 7 days, during which the would write in a detailed "diary" type booklet what they listened to , when they listened, and where they listened.
Studies have shown that the vast majority of participants give responses as accurately as they can.
The methodology is accurate enough to be accepted by an industry group made up mostly of people from the advertising industry... the ones who used that information to invest millions of dollars in radio ad buys.
In the biggest markets, Nielsen now has a "panel" that can have families / households participating for up to and sometimes over 2 years. Measurement is done by a passive device that detects what is being listened to through the detection of sub-audible codded data streams which can be broadcast as many as 12 times a minute, all day long. Participants get quite significant incentives.
Google AI says:
The Nielsen Personal Meter, also known as the Portable People Meter (PPM), works by detecting hidden audio codes embedded in broadcast audio signals from TV and radio stations. Panelists wear the device, which logs the codes to measure media consumption. The data is then sent to Nielsen, which combines it with other households' information to generate ratings.
How it works
- Audio-coding: Radio and TV stations embed inaudible, unique codes into their broadcasts.
- Detection: The wearable meter detects these codes in real-time when worn by a panelist.
- Logging: The device records which station was being listened to and for how long.
- Data transmission: The meter transmits the collected data to a base station at home, which sends it to Nielsen nightly.
- Data analysis: Nielsen combines the data from all participating households to create audience ratings for TV and radio.
How it's used by participants
- Wear the meter: To be counted, the participant must wear the device throughout their day.
- Keep it on: A blinking green light indicates the meter is working and recording.
- Charge it: The meter is placed on a base station overnight to charge and upload data.
- View messages: Tapping the screen allows participants to check messages and see how many points they have earned.
- Earn rewards: Participants earn points for consistently wearing the meter, which determines their monthly payment.
- Personal use: Each person in a participating household receives their own meter, and it is important to not use someone else's device.