Researchers planted lawn signs in randomly selected voting precincts, and then studied the effects. | AP Photo Lawn signs can swing an election, study finds

All those political yard signs littering neighborhoods at election time may not be accomplishing that much, a new study found — though perhaps enough to swing a close election.

Four randomized field experiments in a study by lead author Donald Green of Columbia University and several others found that lawn signs increase voter share by 1.7 percentage points on average, a positive increase, but not a large one.


"It appears that signs typically have a modest effect on advertising candidates' vote shares — an effect that is probably greater than zero but unlikely to be large enough to alter the outcome of a contest that would otherwise be decided by more than a few percentage points," the researchers wrote.

Alex Coppock, one of the co-authors of the study, told POLITICO the effects they found were in persuading voters to choose a certain candidate, not on turnout.

"We were surprised by these findings, because the conventional wisdom is that lawn signs don't do much — they're supposed to be a waste of money and time. Many campaign consultants think that signs 'preach to the choir' and not much else," Coppock said.

"The effect is small in terms of percentage points, though the implication is that thousands of voters would have voted for someone else if not for the signs," Coppock said. "My guess is that part of the reason that the effect is small is because any campaign tactic — signs, ads, mailers, calls, etc — only move people around at the margin. In many ways, it would be strange if the effect were bigger. Imagine a world in which the presence or absence of lawn signs could swing an election by 10 points."

The authors worked in collaboration with a congressional candidate, a mayoral candidate, an independent expenditure campaign directed against a gubernatorial candidate, and a candidate for county commissioner. They planted lawn signs in randomly selected voting precincts and then studied the effects.

Signs placed in the first two experiments were more traditional in scope, though the first experiment placed signs on public lands and the second did so in private lawns. The third experiment was a sign paid for by a 501(c)(4) and was a negative ad for a Virginia gubernatorial candidate. The fourth experiment took a more traditional route, though it featured two candidates and used a picture of an elephant rather than the party name.

"This finding puts lawn signs on par with other low-tech campaign tactics such as direct mail that generate reliable persuasion effects that tend to be small in magnitude," researchers said in conclusion to the study.