The amount of original programming on advertising-supported cable networks hit an all-time high during the fourth quarter of 2008, the Cabletelevision Advertising Bureau said Monday.

The CAB counted 1,837 original cable shows, which account for two-thirds of all ad-supported cable programming. In the fourth quarter of 2002, there were only 725 original shows on cable.

The growth in original programming is a key factor in increasing viewership for cable at a time when ratings at the broadcast networks are falling.

Ratings for ad-supported cable networks are 10.9 points higher than broadcast for the current season, the CAB said. The CAB has cable with a 35.3 household rating and broadcasters with a 24.4.

Among adults 18 to 49, cable’s ratings are up 5.1% this season and broadcast is down 8.3%, compared to a year ago, the CAB said.

“The pace of viewers’ flight to cable has surged dramatically over the past year,” said CAB President-CEO Sean Cunningham. “Advertisers in search of the right kind of value to achieve their goals in a tough environment will ever increasingly depend on their own flight to more cable brands and programming.”