AUDIE CORNISH, HOST:
Tonight is the end of Jay Leno's long run as host of NBC's "Tonight Show."
MELISSA BLOCK, HOST:
It's also the end of a chapter for Robert Lichter.
ROBERT LICHTER: I direct the Center for Media and Public Affairs at George Mason University. Since the late 1980s, we've been tracking political humor on late night television.
BLOCK: And for Lichter's team, tonight means no more Leno jokes to study.
CORNISH: For years, Lichter's team has pored over the late night shows, but not Lichter himself.
LICHTER: I go to bed too early.
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CORNISH: It's his students who have been recording all those opening monologues.
LICHTER: This is like a treat for our best student coders. We let you laugh at the jokes while you're taking them down.
BLOCK: They found in all that cataloguing that many of Jay Leno's jokes had one particular target.
JAY LENO: That one person that brings it all together. That one person becomes the focus of what you're doing. Of course, for me, that person: Bill Clinton. God bless him.
LENO: Where would I have been? Oh, my God...
LICHTER: Leno's favorite target by far was Bill Clinton who accounted for over one out of every 10 jokes about all topics over the last 20-some years.
LENO: You know, we've done so many jokes but Bill Clinton and I really have a lot in common. He was elected in '92. I started in '92. He's still married to his first wife. I'm still married to my first wife. I smile when I sit behind my desk. He really smiles when he sits behind his desk.
CORNISH: According to Lichter's math: over 4,000 Bill Clinton jokes.
BLOCK: And those numbers aren't lost on Leno.
LICHTER: Jay has actually in the past acknowledged our study. He mentioned that he heard some people track these things, and sort of shook his head and suggested that it's just a pretty weird thing that anybody would actually take his material that seriously. And it is.
LICHTER: We are pretty weird for taking this stuff seriously for so many years.
BLOCK: Tonight in his last show, Leno may even make one last Clinton joke for old time's sake.
CORNISH: And Robert Lichter might even stay up to count it.
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BLOCK: You're listening to ALL THINGS CONSIDERED. Transcript provided by NPR, Copyright NPR.