More by what they fail to report than what they actually report. And a lot of bush/rightwing apologia goes unchallenged.
See this FAIR article from 2004:
http://www.fair.org/index.php?page=1180That NPR harbors a liberal bias is an article of faith among many conservatives.... <snip> Despite the commonness of such claims, little evidence has ever been presented for a left bias at NPR , and FAIR’s latest study gives it no support. Looking at partisan sources—including government officials, party officials, campaign workers and consultants—Republicans outnumbered Democrats by more than 3 to 2 (61 percent to 38 percent). A majority of Republican sources when the GOP controls the White House and Congress may not be surprising, but Republicans held a similar though slightly smaller edge (57 percent to 42 percent) in 1993, when Clinton was president and Democrats controlled both houses of Congress. And a lively race for the Democratic presidential nomination was beginning to heat up at the time of the 2003 study.
Partisans from outside the two major parties were almost nowhere to be seen, with the exception of four Libertarian Party representatives who appeared in a single story (Morning Edition , 6/26/03).
Republicans not only had a substantial partisan edge, individual Republicans were NPR’s most popular sources overall, taking the top seven spots in frequency of appearance. George Bush led all sources for the month with 36 appearances, followed by Defense Secretary Donald Rumsfeld (8) and Sen. Pat Roberts (6). Senate Majority Leader Bill Frist, Secretary of State Colin Powell, White House press secretary Ari Fleischer and Iraq proconsul Paul Bremer all tied with five appearances each.
Senators Edward Kennedy, Jay Rockefeller and Max Baucus were the most frequently heard Democrats, each appearing four times. No nongovernmental source appeared more than three times. With the exception of Secretary of State Powell, all of the top 10 most frequently appearing sources were white male government officials.
Other recent FAIR articles on NPR:
http://www.fair.org/index.php?page=13&as_field_all=1&as_keywords=npr&x=11&y=11&as_order_by=order_date&as_order_by_direction=DESCNote also that I'm speaking of NPR
news shows only. Other Public Radio is fantastic (prarie home companion, this american life, fresh air, etc.)