Roberta Kwock writes in “How Much Do Campaign Ads Matter?” at KellogInsight that research indicates that “TV ads do influence voter turnout and choices—and that the tone of the ad makes a difference. Based on data from the 2000 and 2004 presidential elections, the team found that positive ads encouraged more people to show up on Election Day, while negative ads slightly suppressed turnout. And while both types of commercials affected whom people supported, the negative ones were more effective at swaying voters’ decisions.”

OK, that data is 24 and 20 years old. But it did come from 75 markets areas and 1,607 counties.. And don’t forget that campaign videos have found even more exposure on notebook screens since then, and human psychology hasn’t changed all that much.

However, Kwock adds that “research on voter turnout has produced mixed results. Somestudies that evaluated the overall influence of ads, without distinguishing between positive or negative ones, found that the commercials didn’t affect turnout. Among researchers who analyzed specific ad types, some reported that both positive and negative commercials had little effect; others found that negative ads boosted turnout; and still others that negative ads decreased turnout.

Further, “if ads don’t affect voters much, that would mean that campaigns are wasting billions of dollars on every election cycle. But political teams clearly believe that these commercials are worthwhile.”

The effects can be pretty small. “If a candidate increased their positive advertising by 1 percent, voter turnout rose by 0.03 percent. If they increased negative ads by the same amount, voter turnout dropped, but only by 0.007 percent.” Of course elections can be decided by tiny margins. But campaigns often have limited budgets, and cost-effectiveness still rules ad decisions. Nearly all campaigns will have a mix of positive and negative ads.

In February, Jessica Piper wrote at Politico that “Some political ads work a lot better than others. But nobody really knows what will reliably make an ad click with voters….That’s one of the major findings of a new study from researchers who analyzed data from Swayable, a platform used by Democrats to test the effectiveness of different messages and advertisements.” Further,

However,

What makes it particularly challenging is that trends that appeared in one cycle did not always persist to the next. For example, ads that highlighted issues — broadly, any issue-focused messaging — were more effective than other ads in 2018. But in 2020, issue-focused ads in congressional and Senate races were less effective than other ads, which included spots focused on character or biography. Ads with a positive tone seemed slightly more effective in 2018 and less effective in 2020, although not by statistically significant margins in either case.

But Piper cautions:

Still, the biggest lesson for all campaigns may be to not rely too much on what worked in the past….In 2020, some of the most effective ads tested for the Biden campaign were direct-to-camera video testimonials — featuring everyday voters shot as if they could be on Zoom, rather than slick campaign ads. But the style and substance of ads will likely be dramatically different this year, said Nate Lubin, an ad consultant on Biden’s 2020 campaign, even if the presidential race is poised to be a Biden-Trump rematch.

If you want to get wonky abut it, check out “Political Advertising and Election Results” by Jorg L. Spenkuch and David Toniatti, who write in a footnote and graph-rich article at economics.harvard.edu: