The three letter answer is "P P M." Now that a meter is being used (as opposed to writing in a diary), certain formats have benefited and others have suffered. Spanish language formats are in that latter group - probably more than any other type of format. Spanish language listeners have tended to over represent the time listening to their favorite stations in diaries. Perhaps it's out of loyalty, perhaps it's cultural, or perhaps there's another reason. But, once the PPM technology was rolled out, most Spanish stations dropped.
Now, we could argue all day as to whether the Hispanic audience is being properly sampled by PPM. Arbitron says yes. Besides, any variation in sampling probably wouldn't account for that big of a plunge. Basically, in the past, ratings for many Spanish stations have been somewhat inflated.
Remember, Philadelphia is not a significant market for Spanish media. The percentage of the population that is Latino is small and most of them are Puerto Ricans who are more apt to listen to the same stations as everyone else. That's why Rumba danced itself into oblivion within a few months. For a number of reasons, there's no ratings (or money) for that sort of programming in Philly.
