FORTUNE — Nobody in Ohio will be surprised by the fact that the presidential campaigns are spending about $1 billion each on TV spots, most of them negative, and most of them running in nine swing states. That means the campaigns are spending about $1,000 on each “persuadable” voter, Ken Goldstein, president of Kantar’s Campaign Media Analysis Group, told NPR.

Is it worth the expense? No, says political scientist Diana Mutz, who told NPR that there is “very little evidence that the ads make much of a difference.”

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The “much” in that sentence explains why the money is spent anyway. The ads make some difference, though how much of one can’t be quantified with precision. But if your opponent is buying TV time, you must as well. And if he or she buys more, you must buy more. It’s similar to the arms race, wherein the superpowers kept building up their nuclear arsenals long after each one of them had become able to blow up the world several times over.

Last week, Adobe ADBE released the results of a survey showing that people believe television to be the most effective advertising medium. Two-thirds of respondents said TV spots (and, interestingly, print magazine ads) are better than online ads, which 68% of respondents find annoying.

But that doesn’t mean people like advertising of any kind. The survey also found that just 13% of respondents believe that the marketing profession benefits society. Another profession came out ahead of marketers, at 18%. You guessed it: politicians.