This Mitt Romney ad criticizes Barack Obama policies endorsed by the conservative Chamber of Commerce. Whatever works.

With voting just four days off in the United States, the presidential campaigns are digging in for their last chance to convince voters, and they’re being nasty about it.

A full 99% of Republican nominee Mitt Romney’s advertisements had a negative tone in the week between October 24 and 30, as did 85% of President Obama’s campaign spots, according to data from Kantar Media published by Politico. (The remaining 1% of Romney’s ads included positive appeals to Latino and women voters.) Independent political committees also leaned critical, with 89% of Republican ads and 87% of Democratic ads scoring as negative.

Sadly for all the citizens in the swing states that bear the brunt of this onslaught, there isn’t much evidence that all this negativity is actually doing any good. Despite the popular cynicism that “negative ads work,” a review of the political science literature suggests little evidence that negative ads really move voter opinion: “All told, the research literature does not bear out the idea that negative campaigning is an effective means of winning votes, even though it tends to be more memorable and stimulate knowledge about the campaign.”

If anything, the concentration of negative ads is the result of an arms race. One time that political ads seem to work is when one candidate has the spending advantage, drowning out the other’s message. That creates an incentive to match each other’s ads. The two sides, including independent political committees, have each spent about $55 million on advertising during the most recent week measured by Kantar Media.

At least one attack ad showed some creativity, with Democrats creating a fake newscast depicting the world 100 days into a hypothetical Romney administration. Given the amount of spending going into this debate, perhaps we’ve stumbled across a useful campaign finance reform: Half of all campaign revenue should be used to create a blockbuster science fiction film depicting the dystopia created by an opponent’s administration. Then we could get most of the negativity over with in two hours at the cinema rather than weeks at home.

Correction (Nov. 2): An earlier version of this article incorrectly compared spending on campaign ads to the damage caused by Hurricane Sandy. The latest estimates of damage from the storm are in the tens of billions, far exceeding money spent on negative ads last week.

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