UPDATE, THURSDAY PM: Some of those increases in ad clutter were’t as egregious as MoffettNathanson Research’s Michael Nathanson first thought, he says today in a correction to his analysis. The data he received from TiVo “incorrectly calculated the number of commercial minutes,” he says in a note. That included “a massive error” for Fox Broadcasting: Its ad load in Q4 was “flat-to-slightly down” — not up 12% vs the period in 2013. He adds that the calculation for Viacom didn’t count all of its networks. A complete tally shows ad time up “mid-to-high single digits” vs the +8% he reported. And Discovery was “up low-single digits,” not +5%.

Although the corrections don’t change the basic thrust of his piece, he says that from now on he’ll compare the data from TiVo against Nielsen Monitor Plus.

Bernstein Research’s Todd Juenger, who also used TiVo data, says he calculated his numbers differently and is “completely confident in the report, our methodology, and conclusion.”

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PREVIOUS, WEDNESDAY AM: Bernstein Research’s Todd Juenger calls it “desperate,” and MoffettNathanson Research’s Michael Nathanson calls it “dangerous.” But both analysts, using data from TiVo, say this morning that the trend is unmistakable: Major TV network owners led by Viacom, A+E, and Discovery significantly increased the amount of prime time commercial minutes in their shows in Q4, helping to compensate for a decline in viewing.

It’s an important consideration for investors as they await media companies’ Q4 financial results — and views about whether digital platforms are beginning to siphon ad dollars from TV. Increasing clutter is short-sighted, Juenger says, because “viewer engagement is certainly reduced” leaving buyers reaching the “brain-dead.” And that “doesn’t seem like an attractive audience target for many brands, except maybe certain infomercial products.”

He singles out Viacom, A+E and Discovery as “the worst offenders” among major cable network owners when you factor out sports and kids programming, with commercial time increases of more than 3.5% vs the last three months of 2013. Time Warner “was close behind,” particularly at Adult Swim and TBS. Indeed, Viacom and A+E accounted for nine of the 10 most ad-loaded cable nets. Leading the list are CMT (with 109.1 prime time commercial hours in the quarter), Lifetime (98.6), MTV (98.4), TV Land (97.4), and VH1 (95.5). [It should be noted that Juenger is one of Viacom’s most vigorous critics.]

Nathanson — who has identified the ad clutter problem before — also observes that it’s easy to become hooked on the strategy and to keep adding spots to cover up for weak programming. As radio companies discovered a decade ago, “once the genie is out of the bottle, it is nearly impossible to put it back in.”

Among the broadcast networks, his tally shows that Fox increased commercial time by 12%, with CBS +1% while ABC was down 2% and NBC dropped 7%.

But in cable “the most aggressive network owners were those with the worst ratings trends,” Nathanson says. His measure of commercial time showed Viacom +8% (with its target demo C3 audience down 15%), A+E +6% (audience -24%), Discovery +5% (audience -6%), Scripps Networks +2 (audience -4%), and NBCUniversal +2% (audience -13%).

The only company that cut airtime for ads was Disney, -4% even though its cable audience was down 5%.