How differently will men and women vote in this year's presidential election?
It's hard to say, but if history tells us anything, there will be a difference between men's and women's voting choices and views on certain issues. Such a "gender gap" has existed in American elections since at least the mid-20th century.
University of Arizona political scientist Barbara Norrander has spent three decades studying elections, political parties and public opinion. Her research involves studying the gender gap in elections at all levels. Norrander is a professor of political science in the UArizona School of Government and Public Policy in the College of Social and Behavioral Sciences.
The media began covering the gender gap closely in 1980, Norrander said, during Republican nominee Ronald Reagan's winning challenge to the incumbent, Jimmy Carter.
In that election, 47% of female voters chose Reagan, while 55% of male voters did, for a gender gap of eight points, according to the Center for American Women and Politics at Rutgers University – a source that many political scientists such as Norrander rely on for data they use in their research.
"At first, the media focused on why women weren't voting for Ronald Reagan as much as men, and they looked at what they thought would be gender issues, such as abortion," Norrander said.
But Reagan's election wasn't the first time political scientists had seen a gender gap, Norrander said, and issues such as abortion weren't really what drove it. As far back as the 1940s, Norrander said, researchers had found that issues of government-sponsored compassion – such as welfare and international aid programs – received more support from women than men.
Those issues translated into different choices on the ballots.
In the 1950s, researchers found that women turned out more in favor of Republican candidates. The Center for American Women and Politics found that 42% of women identified as Republican in 1956, compared to only about 35% of men that year, for a gender gap of eight points. By 1996, that gap had flipped and widened: Only 33% of women identified as Republican compared to 45% men, for a gender gap of 12 points.
The gender gap persists today, with the 2016 presidential election bringing the widest gender gap since 1996. Donald Trump received 41% of the female vote compared to 52% of the male vote, for a gender gap of 11 points.
The compassion issues that determined the gender gap decades ago are still important now, Norrander said. For example, ensuring everyone has health care and providing economic aid continue to stand out as issues that help people decide how to vote.
"It's those kinds of issues where women tend to be more supportive than men, in part because women make less money than men, and women also are more likely to be in jobs that are associated with these compassion issues," Norrander said.
The gap doesn't just appear in voters' choices, Norrander said, adding that women also vote at a higher rate than men – about two or three percentage points more, according to data going back to about 1980. Determining why this particular gender gap exists isn't as easy as pinpointing what's behind the gap in candidate choice, she said.
"The explanation that I've seen that seems most likely is women have a stronger sense of civic duty (and) that they believe more strongly that people should vote," Norrander said, but she added that it's hard to say why that would be.
For this year's election, Norrander said recent survey data and news reports have indicated that many women view some of Trump's behavior as offensive. That suggests the gender gap between men and women who vote to re-elect the president could widen. However, Norrander said, it's hard to say for sure. Trump's behavior didn't appear to be a big factor in 2016, when white women turned out in large numbers to vote for him, albeit at about 10 percentage points lower than the rate that white men did.
One thing that decades of research has consistently shown, however, is that women do not automatically vote overwhelmingly for a female candidate – such as Kamala Harris, Democratic presidential nominee Joe Biden's running mate.
"It's more of a journalistic impression that women can be talked into supporting a female candidate, but that's not necessarily true," Norrander said. "It's more complicated than that."