But it does not say about radio. The concentration is more on viewership. https://en.wikipedia.org/wiki/Portable_People_Meter https://en.wikipedia.org/wiki/Port

But it does not say about radio. The concentration is more on viewership. https://en.wikipedia.org/wiki/Portable_People_Meter https://en.wikipedia.org/wiki/Portable_People_Meter Edit: This is the link inside that article, which leads to http://www.colemaninsights.com/sites/colemaninsights.com/files/reports/The%20Impact%20of%20Commercials%20on%20the%20Radio%20Audience%20-%20September%202006.pdf http://www.colemaninsights.com/sites/colemaninsights.com/fil... So I think they select random people to carry their device, which listens to radio stations tuned in by the user. Radio stations are identified by the embedded sub-audible codes. The device then phones home conveying the metadata. Interesting. Thanks.