Analysts have stopped telling clients to wait for more data before they worry about the lousy early ratings for the major networks’ primetime shows. Although “it is probably too early to panic, there are several areas of concern,” Nomura Securities’ Michael Nathanson says this morning. That’s a shift from a few weeks ago when he called the initial ratings figures “disappointing” but possibly the result of quirks in this year’s schedules. The new conventional wisdom is that the major broadcast networks have a serious problem as the latest so-called C3 ratings (those who watch a show’s commercials live and as much as three days after they air) show ABC -15% this season vs the same period last year with CBS -23% and Fox -28% — but NBC +12%. RBC Capital Markets’ David Bank said last week that “our best ‘experts’ tell us that it’s realistic to expect ratings for the Broadcast Year 2012/2013 to decline ~5%-10%.” And all eyes are on CBS, which depends on the performance of its broadcast network more than its rivals at Disney, Comcast, and News Corp. CBS shares are down 10.5% over the last 30 days, far more than the benchmark Standard & Poor’s 500 which is -1.8%.

Nathanson says broadcasters are partly to blame for their ratings losses: too many of their new shows are stiffs. The fall offerings are “shaping up to resemble the Yankees’ batting success during the recent ALCS: a lot of swings and just about as many misses.” But it isn’t just new shows that are failing to connect. Investors “should be concerned about the impact of future syndication profits as many returning shows (e.g., Blue Bloods, The Good Wife, Private Practice, Grimm) are at dangerously low ratings levels, and we just don’t see massive bidding wars breaking out” when they hit the market, Nathanson says.

Where are the viewers going? That may be the most worrisome question for TV execs because many people appear to be leaving the TV ecosystem entirely, Nathanson says. The total number of Live+Same Day primetime viewers (at least among the 18-49 demo that advertisers covet) is -4% for the major broadcasters and basic cable networks combined thus far this season. But there’s no simple explanation. Part of the drop can be attributed to Nielsen’s recent 1% reduction in its count of TV households. (More likely due to lack of housing formation in a weak economy than to pay TV cord-cutting.) Researchers will have a field day figuring out where others went. Meanwhile, Nathanson warns that the combination of falling ratings in a weak ad market “could be a brutal and unforeseen combination.”