Will Shapiro help Harris win Pa.? Here’s what the research says.

Political science research is clear: If you want to win the electoral votes of a particular state, it makes no sense to choose a vice presidential candidate who will rely on it.

Unless you’re talking about Pennsylvania, which was decided by about one percentage point in the last two presidential elections — and where there’s a sturdy local political culture.

Kyle Kopko, a political science professor at Elizabethtown College in Lancaster County, knows better than most. He and Chris Devine, who teaches at the University of Dayton, have written two books on the impact that vice presidential choices have on campaign outcomes, including whether choosing a vice president gives a candidate an advantage in his or her home state.

His research suggests that if Vice President Kamala Harris chooses Pennsylvania Gov. Josh Shapiro, it may not make much of a difference.

“We analyzed the effect of home state using a range of methods. In most cases, the result was not statistically distinguishable from zero,” Kopko said.

The truth is that while voters often say they care about the vice presidential pick, very few say their vote was motivated by the vice presidential pick. The candidates’ positions on economic and social issues are far more significant than the No. 2 pick.

“Ultimately, people choose a presidential candidate and evaluate the lists based on that,” Kopko said.

That’s not to say vice presidents don’t matter. First, there are second opinions: Political analyst Nate Silver calculates an augment of 0.4% in the home state of the vice presidential candidate, which could certainly make a difference in a tight state like Pennsylvania.

There’s also evidence that vice presidential choices can affect campaigns in other ways, reflecting a candidate’s judgment or ideology. For example, Kopko’s data shows that negative media reaction to then-Alaska Gov. Sarah Palin lowered perceptions of Republican candidate John McCain’s candidacy in 2008. But that effect was nationwide. It wasn’t narrow to a particular state.

Still, there are only a few cases where a local vice president can make a difference. “If you have a relatively small state and the candidate has a lot of experience representing that state, you might see a signal,” Kopko said.

Again, 2008 provides a helpful example. That year, Kopko said, then-Sen. Joe Biden really moved the needle for Democratic candidate Barack Obama’s campaign in Biden’s home state of Delaware. That’s because Biden was a particularly large fish in a tiny Delaware pond, and voters there responded with appropriate enthusiasm to the favorite son.

There are also counterfactuals: While Obama didn’t really need Biden’s help in the Democratic state of Delaware, Kopko suggested that if former Vice President Al Gore had picked then-New Hampshire Gov. Jeanne Shaheen in 2000, it might have been enough to secure New Hampshire’s electoral votes — and the presidency.

Shapiro may not be in the same category. He hasn’t been on the scene as long, and in any case, Pennsylvania is a much bigger place than Delaware.

Unless Pennsylvania is a completely different place.

Berwood Yost, who directs the Center for Public Opinion Research at Franklin & Marshall College, acknowledges the validity of Kopko’s research but suggests another possibility.

“There’s something to be said for Pennsylvanians that they value their local communities and where they’re from,” Yost said. “They don’t say, ‘I’m from Pennsylvania.’ They’ll say, ‘I’m from Pittsburgh,’ or ‘I’m from Hershey.’ And at least in primary elections, that local element definitely has an impact on voting.”

Yost cited a number of facts: Even in an era of nationalized politics and intense partisanship, Pennsylvanians still show a high degree of regional loyalty when voting — hardly surprising in a state with one of the lowest rates of in- and out-migration in the country.

He believes that this local element could make Pennsylvanians more likely to get excited about a popular local politician, even if he is the No. 2 candidate.

He also noted that the last time a Pennsylvania official was nominated for vice president was in 1844.

“Pennsylvania isn’t even included in Kopko’s data,” Yost said. (Kopko’s research goes back to 1884.)

Kopko acknowledged that whether Pennsylvania is unique or not, there are some unique dynamics at play in this election.

“More than in other years, Harris continues to present herself as the presumptive nominee,” Kopko said. “For that reason, the introduction of the vice president may have a greater impact than usual on the tone of Harris’ campaign.”

But again, that effect could be felt across the country. Not just in Pennsylvania.

That’s not to say Kopko thinks there aren’t circumstances in which Shapiro’s election could make a difference in November. “If we have a situation like Florida, it could make a difference,” Kopko said, referring to the historically close 2000 election. “There may be a few hundred people who [would have] voted for Harris because she chose Shapiro.”

Pennsylvania elections are close, but they usually aren’t. This close. “At a margin of tens of thousands,” Kopko said, “I would doubt that’s a variable that makes a difference.”