Maybe this is why Romney is so reluctant to go on late night shows: he's been joked about more than twice as much as the president has. The Center for Media and Public Affairs took a look at who late-night hosts targeted between August 27 and October 3. While Obama was the target of only 62 jokes in monologues by Jay Leno, David Letterman, Craig Ferguson and Jimmy Fallon, Romney took 148. On Letterman's show Romney got almost five times as many jokes as Obama. Letterman, Bill Carter wrote in The New York Times, "has waged an on-camera campaign to get Mr. Romney onto his visitors’ couch, at one point even telling his viewers not to vote for the Republican unless he turned up." One gets the sense Letterman knows his jokes haven't been very unbiased given this segment surmising why Romney hasn't been on:

Now some caveats: This study, which looks at the "highest rated late night talk show hosts on the broadcast networks," does miss some late-night shows like Jimmy Kimmel's on ABC and Conan O'Brien's on TBS. Also, concluding the study October 3 misses the fall out from Obama's poor performance in the first debate.