MediaBuyerPlanner: ABC's Nightline has finished ahead of CBS's Late Show with David Letterman in total viewers and adults 25-54 for four out of the past six weeks.

The trend began in June, when Nightline tied new episodes of Letterman in ratings among adults ages 25-54 and adults ages 18-49. The show then beat Letterman episodes in total viewers for three weeks in a row in August.

Nightline's audience is up 9 percent compared to a year ago, following a revamp that added lighter features and more celebrity coverage while continuing to maintain the show's news focus with frequent segments on political and social topics.

Letterman, meanwhile, is down 5 percent from last year's 4.3 million viewers, writes Media Life. Letterman recently signed on for four more years with CBS, bringing his contract through 2010, one year after NBC rival Jay Leno leaves the air, according to the article.