In a rare occurrence, cable's ad-supported cable networks have lost viewership in the initial weeks of a new fall TV season versus that of the previous year.

In the first three weeks of the season -- September 21 to October 11 -- cable lost 5% among its three major demographic groups: 18-34, 18-49, and 25-54 viewers, according to new research from media agency group Group M using Nielsen Company data.

Cable network viewers 18-34 dropped to a collective 15.34 million, down 5.2%; the 18-49 audience went to 16.95 million, off 4.7%; and 25-54 viewers sank to 4.6% to 18.08 million.

Virtually all the loss came from cable news networks, which are witnessing lower ratings as a group versus that of the big upswing in viewers a year ago, due to the presidential election. Cable news networks have lost a massive 61% of their 18-49 viewers as a group and 54% of their key 25-54 viewers as a group.

Taking out those news networks -- Fox News, CNN, MSNBC, CNBC, and Headline News -- other cable networks are seeing virtually flat viewership with a year ago.

"Looking at the first three weeks of the season, this only happened once in the last six years, and that was in 2006-2007," says Lyle Schwartz, managing partner and director of implementation research and marketplace analysis for Group M. "But by the end of that 4th quarter [ratings] had rebounded to basically flat, which is probably what will happen again this season."

Broadcasters don't have much to cheer about in all of this. The five-network average shows declines as well -- 4% slippage in each of its main view categories -- 18-34, 18-49, and 25-54 -- sinking to 9.29 million; 11.23 million, and 13.12 million viewers, respectively.

Taking out sports from the networks brings worse results. For example, broadcast networks lost 6% of their 18-49 viewers of the period.

The only gainers so far after three weeks: pay TV and PBS. Pay TV gained among younger viewers -- with a 6% hike for viewers 12-34, as well as being up 6% among 18-34 viewers. Pay TV also climbed among older 25-54 viewers by 2%. So far, PBS has also pointed up, with a 6% hike among 12-34 viewers, a 5% improvement among 18-34 viewers, a 4% gain among 25-54 viewers, and a 3% increase among female 18-49 viewers.

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