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Apparently I've got this wrong. Baumol's Cost Disease is a theory in dispute. I just googled "Baumol's Cost Disease Arts" and found:

The first link is to the wp article. The second is an Amazon listing for a book called Baumol's Cost Disease: the Arts And Other Victims. (http://www.amazon.com/Baumols-Cost-Disease-Other-Victims/dp/...). The author is apparently an economics professor at a University in England. There's also an abstract from the Journal of Cultural Economics. Baumol apparently developed his claim in the 1960s by looking at the economics of the performing arts, and then generalized it to education and health care.

http://www.springerlink.com/content/k16p700536510057/

At the top of the second page is a New Yorker article that certainly would have made a better HN submission:

http://www.newyorker.com/archive/2003/07/07/030707ta_talk_su...

But apparently, the jury is still out. Google also turns up links to skeptical papers:

"Has Baumol's Cost Disease disappeared in the performing arts?"

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi...

and

"Why I do not Believe in the Cost Disease"

http://www.springerlink.com/content/xuegr8k39y17t3nq/

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