After I did my previous post, I discovered that Timothy Larsen had done his own informal survey of NPR and wrote about it in the current issue of WORLD.
(Note to self: Read your own magazine first.)
Larsen's analysis is not scientific, but he makes some good points. His main point is that NPR programs have a decided absence of Christian voices. Here his article:
http://www.worldmag.com/articles/17812