Labeling a program a special is just one technique. Networks typically “special out” a show when they expect it to fare poorly, against the Super Bowl , for example. Other strategies include front-loading national commercials early in a show and extending the program lengths for hit shows a minute or two into the following hour.

“There’s a lot of chicanery,” said Brad Adgate, the longtime director of research for Horizon Media, which buys time on television shows. “It’s a way to tweak your opponents and get some ink for yourself.”

NBC took the opposite path of ABC with the use of the term “special” in its presentation of the Republican primary debate on Jan. 23. Careful viewers noticed that the debate was labeled a regular edition of the network’s ratings-challenged newsmagazine program, “Rock Center with Brian Williams ” — one that, as it turned out, just happened to double the show’s usual audience to just over 7.1 million viewers.

The one-week ratings increase for “Rock Center” will most likely not alter its future — it lost half that audience a week later. But in a time of declining viewership, it means that the program’s average rating for the season may tick up a tenth of a rating point or two. And, especially at the bottom-rated NBC, that matters.

Networks closely track the gimmicks their competitors use to lift ratings, and it is a hotly debated subject within the industry, but most executives avoid speaking publicly about it so as not to be critical of tactics that they sometimes use themselves.

ABC executives defend their “Good Morning Amer” ploy by pointing out what happened in 2005, when “G.M.A.” came close to breaking the 16-year-long weekly winning streak of the “Today” show. NBC saved the day with a last-minute Friday morning stratagem: playing all its national commercials in “Today’s” higher-rated 7 a.m. hour — meaning its less-watched second hour did not count that day.

The manipulation of where national commercials are placed in a show has become one of the favorite shell games networks use to try to enhance their numbers. Shows receive national ratings from Nielsen only up to the point when the last national commercial is broadcast — after that, the numbers simply do not count.

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Perhaps the best example of the legerdemain behind the placement of national commercials can be seen in late night, where what should be a head-to-head competition takes place on a decidedly uneven playing field.

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ABC’s “Nightline” always has enjoyed one advantage over the entertainment shows on CBS and NBC hosted by David Letterman and Jay Leno , because it traditionally compares ratings for its half-hour program against the full hour of the other late-night shows. That gives “Nightline” an edge because in late night, every minute that passes means more viewers are off to bed.

This year, “Nightline” has managed to shift the contest even more heavily in its favor. At least that is how one competitor, Rob Burnett, the executive producer of the Letterman show, sees it.

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“It’s a trick, it’s an obfuscation,” Mr. Burnett said.

“Nightline,” a 25-minute show, is frequently measured for many fewer minutes, often as few as 16, while Mr. Letterman’s show averages more than 48 minutes. By steering all its national commercials within the first 16 minutes of the show, “Nightline” can substantially improve its ratings. (Regardless of when its commercials run, “Nightline” is doing better in general, and if the shows are measured first half hour to first half hour, “Nightline” still edges ahead of Mr. Letterman and Mr. Leno.)

Another ratings tactic that is now routine involves extending the duration of more popular shows, allowing them to run a minute or two past their scheduled end time. That means the show that follows — usually one a network wants to enhance with the best possible introduction — gets a ratings lift in early national ratings reports that are often widely reported by news outlets.

In December, for example, Fox ran its singing competition “The X-Factor” a minute long to provide a strong entry for “I Hate My Teenage Daughter,” the low-rated comedy that followed it.

In the initial national ratings that Nielsen reports every morning, these later-starting shows receive inflated numbers in their first half hour. Those numbers are corrected by the late afternoon, but by then media reporters intent on getting news up as fast as possible, have often bestowed some measure of success on the tagalong show.

“We’re all competitive,” said a senior executive from a network programming department who asked not be identified when discussing ratings tricks. “And we’re going to try to get you guys in the press to write our story.”

Mostly, ratings gimmicks have little financial impact on the networks, beyond giving bragging rights to their executives — and maybe some ego stroking. “They’re getting bragging rights of being able to say they are No. 1 in late night,” Mr. Burnett said of “Nightline.” That’s meaningful for them. They’re monetizing it.”

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Marketers get what they paid for no matter where a commercial gets placed. Conversely, though, some local advertisers are relegated to the back end of shows.

A Nielsen executive, who requested anonymity because of confidentiality agreements with clients, said Nielsen did have guidelines for what could be done with shows, but recognized that networks would “format their programs to generate maximum ratings impact — call it gimmicks, or call it spin.”

Unless the gimmick results in something egregiously false, Nielsen does not step in. The worse that might happen would be a sternly worded letter.

“You do everything you can, as long as you can,” said the network program executive. “And then they slap your hand.”