When you change format, your ratings can immediately go up. When KTLK went liberal talk in 2005 their book jumped. At the same time conservative talker KFI-AM dropped. duh. there are more liberal News/Talk fans in California. But that instant (1Q) gratification is rare.
Your ratings also can drop initially in a period we kindly refer to as adjustment. It could be just that I changed format, and the readers I appeal to shifted, and a recovery period would be required to see a return. I will return to regularly sheduled programming tomorrow, where as a radio station will probably wait a quarter or two before making a panic-driven flip back to their original format. But usually they will tough out a year or more before trying something else. But the change makes sense.
Under format A. your listeners we're primarily female, white 25 - 45 in age. Under format B. They are male hispanic and under the age of 30. There is certainly a common listenership, but they are small and you cannot market to fractions. The ad dollars are in big groups generally. And allowing multiple staitons to fight over the same demo in a market benefits NO ONE. (but it happens)
In Philadelphia, WSNI despite a very stable and respectable book, (averaging a 2.8) they dropped Soft AC and went Tropical last week. Philadelphia is one of few top 20 cities that do not have a latin-focused FM so the change was not entirely unexpected. Philly has a big latino population, but it's 2 generations or more old and very americanized. The decision to go Tropical is a long term decision in this city. WEMG-AM has been running a similar tropical format for years and they haven't had much better than a one share in years. The bet is that WSNI will steal 50% or more of it's listeners from WEMG-AM and then also gain new listener. (If all other things are equal, an FM will outperfrom an AM.) WSNI probably will recover quickly and be back to a 2.5 share by xmas. But is our hispanic population big enough to support two latin outlets? No. WEMG will go Spanish Oldies, Reg Mex. or pick up the Air America programming that didnt' work out on WHAT-AM. (I'm hoping for the libs of course)
As another example: WCBS New York. They dropped oldies and went "Jack" They lost almost their entire audience and dropped two points. They even had picketers It was a gutshot. They've spent a year recovering and WBZO-AM (oldies) in Long island has managed to gain a point in their book (average) in the same period. I wonder where those listeners came from... but they're gambling. They're betting long term that the aging of their demo will eventually result in ratings death. They decided that now was the time that their high operating costs outweighed losses in their ad book. They may lose short term. But long term they will win.
On the other hand ...KZLA flipping from country was just dense. Los Angeles certainly wasn't short on Rap or CHR outlets. I cant' explain that at all.
So will my readership return to normal over the next two weeks? We shall see.