Have Rush Limbaugh's ratings really “doubled,” as the WashPost claims?

Here's what Howard Kurtz writes today:

By one measure, Rush Limbaugh is a clear winner this week: His ratings have nearly doubled since his feud with the White House burst into the media limelight.

Wow, Limbaugh's ratings are up almost 100 percent since January; since Limbaugh first announced he hoped Obama failed.

I don't buy it.

And please note that the Post provides no facts to back up the assertion; no ratings numbers. No nothing to substantiate the claim. How does the Post know Limbaugh's nationwide ratings have “doubled” in the last month? Readers have no idea.

I'm especially curious how the Post knows so much about Limbaugh's ratings success because even people in the world of syndicated radio don't know since they don't have comprehensive rating numbers for February yet. And in terms of truly national rating numbers (as opposed to just the top markets), that information is only gathered quarterly, I believe. Meaning, it would be impossible to tell if Limbaugh's up nearly 100 percent nationwide since January.

Also keep in mind that when the ratings numbers are collected, they're not made public. The only way reporters can get ratings information for syndicated talkers is if their syndication companies want to release it. (Or via advertiser.) In other words, the only way we'd know if Limbaugh's ratings have “doubled” would be if Limbaugh's company said so.

Seems to me if Kurtz at the Post is going to stroke Limbaugh in print and make the sweeping claim that Limbaugh's ratings have “doubled” nationwide, the newspaper ought to back that claim up with independently verifiable information.

UPDATE: It appears that not even Limbaugh knows if his ratings have doubled. Today, Byron York at the Washington Examiner asked the turbo talker about his ratings. This was Limbaugh's response, in full:

The latest numbers I have are for January, well before this kerfuffle began, and they are through the roof -- six shares in NY, for example. There are daily ratings taken now in about the top 15 markets but I have not seen them yet. All I can tell you is that as of January, we booked 80 percent of all our 2008 revenue and we'll be over 2008 by the end of this month.

Limbaugh himself hasn't even seen ratings more recent than January. Yet the Post claims Limbaugh's ratings have nearly doubled since January. What does the Post know that Rush does not?