You will be redirected back to your article in seconds

Since Barack Obama’s inauguration, Fox News Channel has become one of TV’s biggest success stories — registering ratings growth of 30% or more in key primetime and total-day measurements over last year.

That makes FNC a shining star in the News Corp. empire, to be sure, but Fox and its key talent would also have us believe that the surge reflects disenchantment with other media and a shift in the political winds.

More likely, though, it’s just a case of preaching to the same like-minded anti-Obama choir, for greater periods of time. And therein lies the misleading overreach in the argument. Extrapolating from ratings is always hazardous, given the uncertainty of measuring audience sentiment. But drawing sweeping conclusions about the zeitgeist from such data is specious at best.

Nevertheless, Fox titan Bill O’Reilly has repeatedly stated as fact — without supporting documentation — that the channel is thriving thanks to a backlash against corrupt media that are “in the tank” for Obama. Because of that, he contends, “the folks” — including liberals and independents — have turned to Fox News for its trademarked “fair and balanced” coverage.

But based on a review of the available research, a more reasonable explanation is that Fox has simply strengthened its ties to its core viewers, many of whom are watching for longer periods.

Based on this theory, a telling aspect of Fox’s impressive ratings is “length of tune,” or LOT, which documents how long viewers watch a channel before flipping away.

Fox enjoys the longest tune-in among the cable-news channels and has seen those levels grow this year. MSNBC’s LOT has risen as well, while CNN’s has declined.

As for how this translates into ratings, think about radio. Traditionally, people check AM news for traffic, weather or sports scores and then move on. In talkradio, by contrast, listeners stay tuned longer — and stations can thus average higher ratings despite a smaller overall audience pool.

Hence CNN can talk about reaching more people (or a higher “cume”) while attracting a much smaller average audience than Fox, which — along with MSNBC — more closely approximates a talk format, especially in primetime. Indeed, not only have Fox and MSNBC expanded their LOT while CNN’s has dropped, but Fox’s LOT has eclipsed CNN in August by more than 60%.

So Fox has solidified its bond with a disaffected Republican base. The channel has also become more strident in its conservative rhetoric (welcome, Glenn Beck; hello, “Hannity” sans Colmes), offering a less-diluted balm to conservatives in reinforcing their misgivings about Obama.

More subjectively, Fox also has benefited from CNN’s lack of direction. Fox is simply more focused, while approximating the old local “Eyewitness News” approach: livelier presentations, more alarming graphics and more alluring female news readers.

In good news for the sales department, Fox’s tally among adults 25-54 — the key news demographic — rose by a slightly higher percentage than the net’s total-viewer gains; nevertheless, the news audience still skews old. FNC’s median-viewer age remains among TV’s oldest, at 64, with MSNBC and CNN at 59 and 62, respectively.

According to an MRI study, Fox attracts the highest percentage of conservatives and MSNBC the lowest, but all three news outlets draw an ideological mix.

Fox’s growth, however, is primarily driven by big gains in the evening (starting with Beck at 5 p.m. ET), and its audience in that daypart leans heavily right. A Pew Research Center survey found that two-thirds of O’Reilly’s and Sean Hannity’s viewers are self-identified conservatives.

As former FNC host Eric Burns told the Associated Press, Fox “knows its base.” And unlike his earlier life in politics, FNC chairman-CEO Roger Ailes clearly understands that in cable TV, commanding loyalty from a relatively narrow constituency can be a winning formula.

Taking these factors together, the profile of Fox’s success takes shape: Its viewership is tilted toward conservatives, many near or past retirement age, now watching for longer stretches (and paying less heed to CNN) with a Democrat in the White House.

In the process, Fox’s dominance of its niche has grown. The channel’s 2009 average of nearly 2.2 million viewers in primetime ranks among the top cablers overall and easily exceeds the sum of CNN (983,000, down 6%) and MSNBC (845,000, up 20% from a smaller base).

O’Reilly’s two nightly airings currently combine for around 5 million viewers. That’s huge by cable-news standards, but the host shouldn’t try to conflate that into some broader political referendum, given the perspective that nearly 60 million people voted for John McCain in 2008.

So credit Fox with doing terrifically well at a moment in which even modest growth by any mature network marks a genuine accomplishment. It’s only when the channel explores why that’s happening — and translates its Nielsen spread sheet into a populist rallying cry — that the chest-thumping ventures beyond no-spin into all-bull.