Although WBWL was down by a similar amount, which indicates to me that there simply might not have been as many members of this month's Nielsen panel who listen to country music as there've been in previous ratings periods.
Panel changes can effect a station, but generally only if you have much of a larger household listening a lot to one station.
The PPM panel is what I'd call "semi-permanent". While in the diary survey, the respondents report one week of listening and are gone, in the PPM they have a true panel based on households which can remain on the panel for two years. That means that in "a perfect world" the panel changes by about 4% each month.
In fact, it changes more... around 8% average. That is because some people drop off because they get tired of it or move to a different city or the family has a divorce or some other occurrence. Some are removed from the panel because they don't faithfully carry the meter... if even one household member does not comply, the household is removed. And some get on the panel, don't like doing the chore and only last a month or less.
Still, that means that there is not enough panel change each month to remove a big part of a major station's listener base. The fact is that a station with a 4 or 5 share may cume 15% to 20% of the market. That means that a larger share station has a lot of cume and a lot of metered users.
Again, we're talking about decreases of about half a point for two stations playing the same music, not WKLB falling off the edge of the earth with a 3- or 4-point crash while WBWL increases share. As much as many around here may wish that eliminating a disc jockey will always prove foolhardy and cost the offending station listeners and advertising, that's just not the way it's working in modern radio, especially in formats that appeal to younger listeners who prefer to hear music with a minimum of gab.
Yep. Also remember that there are times of the year when radio listening itself changes a bit, such as the month when public schools in a market close for summer or come back for fall. And, of course, between Thanksgiving time and New Year's week. So use of radio changes, and some stations and formats can be affected globally by that change.
Also consider usage of radio if a market has a very winning sports team, causing more interest in sports talk formats and, thus, less music listening by men of nearly all ages. And there are one-time events like a blizzard or storm week or flooding or other event that affects all kinds of normal living in a market. So a real analysis has to take outside influences into account.
And, of course, towards the end of the year Nielsen "months" are spread across two calendar months. In fact, most of the December book is in November!