It's no surprise, then, that as attention has fragmented, the price of a Super Bowl ad has grown even faster than viewership, as this great chart from Bloomberg shows (audience numbers to the left; ad prices to the right, in green).

To understand why the Super Bowl is such a good deal by TV advertising standards, you have to understand the first thing about TV advertising. It's not about the price you pay for the advertisement. It's about the price you pay for the eyeballs.

The argument "$4 million for 30 seconds is absurd" is sort of like saying "$1,000 for dinner is absurd." Yes, $1,000 is an expensive dinner-for-one. But what about a fancy dinner for 10 friends? Or 20 friends? Or 100? The more people at the table, the more that $1,000 starts to look like a bargain.

At least 115 million people will watch the game this year. When you divide a $4 million commercial by an audience of 115 million, you get a "rate" called CPM—cost-per-mille (thousand viewers). The Super Bowl's rate this year is about $35 to reach 1,000 people. Is that expensive? Not at all. Last year, the average CPM for primetime TV was also $35. On a per-person basis, the Super Bowl is the same price as buying a typical 30-second primetime spot any weekday of the year.

But Super Bowl ads aren't like any other ad. They're special. They're celebrated. You actually watch them. People in living rooms across the country say, in unison, "Everybody shut up, I want to experience this corporate messaging so that I can engage with the brand." Okay, so maybe that's not verbatim, but it's the gist. For four hours a year, a Super Bowl viewer transforms from an ordinary human, constantly rejecting the bombardment of advertising, into a marketing professor's platonic ideal of consumer, diligently seeking out great brand messaging. Surely, that remarkable metamorphosis is worth something.

What is it worth, exactly? This is where determining the true value of a Super Bowl ad suggests that the problem isn't the message—it's the medium.

Super Bowl Ads: An Incredible Rip-Off

The question "do Super Bowl ads work?" is a somewhat useless question because it's such a broad category. If somebody asked you, "are movies any good?" or "are TV shows watched?" you would regard this person like an alien, and then, after realizing the question was serious, respond with some variation of "uh, sometimes?" And "sometimes" is the answer to the Super Bowl question, too.

Super Bowl ads work, sometimes. Brain scans of 2006 Super Bowl viewers watching different commercials revealed dramatically different fMRI results for different ads, confirming what you already knew. Some Super Bowl ads are brain-tickling pieces of art. Some Super Bowl ads are toe-curlingly awful.

Even if many of the ads fail, there does appear to be something like a "Super Bowl bump" in the market. The stock prices of Super Bowl advertisers between 1996-2010 increased by $10-20 billion annually for the two weeks around the big game, according to research from the University of Wisconsin, Eau Claire. Another study found "significant abnormal net buying activity," particularly among retail investors, up to 20 days after Super Bowl ads. This brief post-game spike didn't necessarily last longer than a fortnight. But it suggests that, even if viewers don't love all Super Bowl advertisements, investors do.