Season-to-date prime time ratings are down 11% vs last year for the Big Four networks in live-plus-same-day results for their target audience of 18-to-49 year olds. And investors want to know: Is this a blip, or a symptom of a deeper problem — possibly viewer defection to online videos? Two reports out this morning acknowledge the problem but urge investors to wait for more information before panicking about the prospects for the Big Media companies that own the major networks. While it may be cold comfort for moguls, the main problem seems to be something they can address: lousy programs. “Most of the freshman shows have been a disappointment,” says Barclays Equity Research’s Anthony DiClemente. “Without top quality new programs to augment the success of past hits, we believe aggregate network ratings have suffered.”

Still, several factors may have exaggerated the problem. There are the vagaries of the schedule: For example CBS’s decision to move Two And A Half Men from Monday to Thursday “impacts both nights because of last year’s early success on Monday [with the introduction of Ashton Kutcher who replaced Charlie Sheen] combined with the greater competition this year on Thursday,” Nomura Equity Research’s Michael Nathanson says. NFL football also may be tipping the scales: Match ups are stronger this year for Monday Night Football, and the NFL Network added five Thursday Night Football games. (Previously it didn’t begin its schedule until week 10.) That could be taking a bigger bite than usual from live ratings as the number of people who use DVRs to time-shift non-sports programming grows. The audience for shows including Revolution, Glee, The Office and Up All Night is at least 50% higher when you measure viewing up to seven days after they air vs live plus same day results. When Nielsen releases the data that advertisers value most, live-plus-three day ratings, that “will tell a more complete story,” DiClemente says.

But while the additional info will help, “we don’t see it offsetting this year’s higher declines,” Nathanson says. He warns that CBS, which collects 27% of its revenues from broadcast network advertising, is “most exposed” if the ratings drop continues. It would affect 8% of News Corp’s revenues, 7% of Disney’s, and 5% of Comcast’s (which controls NBCUniversal). Put another way, if broadcast network ad sales dropped by 5% due to poor ratings it could cut earnings per share at CBS by 5.7%, News Corp by 2.1%, Disney by 1.3%, and Comcast by 0.7%.