Technology is helping radio stations schedule guests, even callers. The Wall St. Journal wrote about how radio stations use an audience monitoring tool, the People Meter, to make booking suggestions for their programs.
The article, "Radio Shows Tune In to Listener Habits," cited a KPWR program director who decided not to invite back a guest after "realizing the station lost listeners during each of his last three airings on the morning show."
Now a case could be made that it was the topic, not the guest, that turned off listeners.
But the overall case makes sense -- even given some questions as to the accuracy of the People Meters -- that the radio station loses listeners.
PR funcstions should keep this in mind when pitching radio producers. It's not that you'll likely have access to the numbers/ratings. But it's at least helpful to understand that they're looking for ratings on segment-by-segment basis.