The fact that Republicans and Democrats differ on whether health-care reform should include a public option is no surprise. That they differ on setting a date for exiting Afghanistan, sure. On Sarah Palin, of course. But on physics? And biology? That the growing list of issues where there is a partisan divide now includes the accuracy of scientific findings may be lamentable for a democracy (if we can't agree on facts, how can we agree on policy?), but it's a gold mine for research on how personality and other psychological factors influence political ideology.
The red-blue split on mammograms is particularly striking. In a recent poll, the Pew Research Center asked 1,002 American adults about a preventive-health task force's conclusion that most women can safely begin mammograms at age 50, not 40, and have one every two years, not annually. (Large studies have found that earlier mammograms save almost no lives; since the radiation can cause cancer, it therefore makes sense to minimize them.) Among Republicans, 15 percent agreed with that. Among Democrats? Twice as many.
One reason, of course, is that the mammogram wars have become entangled in health-care reform, with accusations that the advice is part of a dastardly plot to ration care. Some of the partisan split therefore reflects red-blue views of what John Jost of New York University, who studies the psychological basis of political ideology, calls "a softer version of the 'death panel' claim." But something else is going on, something that speaks to how traits of personality affect political leanings. Since people do not pore over oncology studies and reach their own conclusion on the credibility of the science, they have to trust experts—or not. And thus the partisan divide: Republicans tend to distrust "elites," especially now that the GOP is more Palin than George H.W. Bush or other scion of the white-shoe establishment. In the mammogram debate, that distrust encompasses pointy-headed scientists and makes those who disdain "the reality-based community," as an aide to George W. Bush called scientists, go with the "common sense" view that mammograms save lives.
There is a long list of personality differences between liberals or Democrats and conservatives or Republicans. The former are generally more open to new experiences and ideas, Jost and colleagues found in a 2003 study. The latter tend to be more conscientious, more energetic, and more emotionally stable, Jost later found, as did a 2007 study of 5,623 voters led by Chris Fraley of the University of Illinois at Urbana-Champaign. The differences are significant: the personality traits predict voting decisions more strongly than age or gender, Fraley found.
The partisan divide on another empirical question—whether Earth is warming, and if so whether that is due to human activities—may reflect something similar. In October, Pew found that 75 percent of Democrats polled say there is "solid evidence of global warming," with 50 percent of those attributing it to human activity. Only 35 percent of Republicans recognize global warming; of those, 18 percent see the hand of man. Obviously, people are not calculating radiative forcing or working through other equations of atmospheric physics themselves. Party affiliation likely makes some people leap from "Is climate changing?" to what to do about it, so Republicans may be blind to climate change just to deny any need for regulation of greenhouse gases. But here, too, psychological factors are at work.
As with mammograms, climate change is also a matter of trust and belief (or not) in experts: physicists, or Glenn Beck? In addition, denying environmental reality reflects, in part, a tendency to justify the existing order, argues Jost. Conservatives, part of whose ideology is to respect and protect the status quo, tend to engage in this "systems justification" more than liberals, tending to view corporations, markets, government, and other institutions as legitimate and benign. Acknowledging climate change means recognizing "shortcomings of the current system" and "admitting that the status quo must change," Jost and colleagues write in a paper to be published early next year. They find that a desire to justify the status quo (gauged by agreement with such statements as "Most policies serve the greater good" and "Society is set up so people usually get what they deserve") accounts for much of the variability in people's likelihood of denying climate change.
It's comforting to believe our views on political and empirical questions are the product of rational thought and analysis. But belief doesn't make it so.