The link below directs to an article from the excellent Minnesota Post on how new devices for monitoring radio listening have deflated the ratings of local talk radio stations.
http://www.minnpost.com/...
The new devices, called PPMs, seem to mirror the change in recording TV viewing habits, in that the PPMs replace written diaries with devices that monitor actual listening (and report statistics automatically). The article observes that local talk radio has lost ratings to music stations as a result.
Undoubtedly, one factor affecting this shift in ratings is that these devices report "background" radio as well as "foreground"--i.e., what the listener hears on a radio playing in a business, as well as what they're actively listening to in a house or car.
But another factor may be the dishonesty factor (dishonesty among talk radio listeners, that is, as opposed to talk radio itself). A listener who agrees with, say, Rush Limbaugh could simply mark in a diary that he listened to Rush all the time. The PPMs call BS on this abuse of the old-fashioned "honor system."
One local AM station spokesperson asserted that his station no longer "sold ratings" and that it relied instead on its relationships with sponsors. As the article implies, this may refer to direct salesmanship by radio personalities ("Folks, I'll open the phone lines to callers in a minute, but first let me tell you where to find the best deals in used cars"). Wonderful. As the relationships between talk radio personalities and sponsors gets tighter, the sponsor is going to think more about what the radio personality advocates. It also becomes more obvious where the screws of boycott need to be applied when the spewage exceeds the bounds of sense or taste.