What Democrats and Republicans don't have in common goes far beyond the ballot box. Their personalities, like their core beliefs and policy ideas, are fundamentally different.

Liberals are creative and curious, and tend to be more open to new experiences, while conservatives are more anxious, dislike change, and appreciate order in their lives. Scientists don't know if political interests shape temperament, or vice versa, but new research suggests lawmakers' personality traits play an important role in political causes—like forcing a government shutdown—and may even determine if those causes survive.

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In a study published this week in the journal Psychological Science, researchers asked 300 people in an online survey whether they agreed or disagreed with both political ("In general, I support labor unions") and nonpolitical statements ("I enjoy coffee"). They also asked participants to indicate how much others who shared their political views would support their attitudes.

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The results showed that liberals underestimated their levels of partisan support; that is, they thought their beliefs were different from their liberal peers, when they actually were not. Conservatives and moderates, on the other hand, thought their beliefs were more similar to those of other members of their political group than they actually were, overstating partisan agreement. These patterns of thinking held for topics unrelated to politics, like personal preference for coffee.

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Real-world politics, however, is where it gets interesting. Democrats, thinking they lack support, struggle to find solidarity, the researchers conclude. Republicans, sticking together because of a perceived abundance of support, get mobilized—and effect change—more quickly.

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This party distinction in judgment stems from yet another fundamental difference between liberals and conservatives: the need to feel unique. In the study, liberals reported a stronger desire for uniqueness than did conservatives and moderates—a strange finding for the party that champions social programs, as well as Republicans who stand for an Ayn Rand individualism.

That thinking, says study coauthor Chadly Stern, a psychological scientist at New York University, can undermine progress. Conformity, at face value, works better. Conservatives, by banding together under one leader, don't waste time agreeing with each other, Stern says. One prime example? The tea party, led by Sen. Ted Cruz, R-Texas.

Democrats, meanwhile, are slow to mobilize. Stern cites the fractured Occupy Wall Street movement as one example, the 2010 repeal of the "don't ask, don't tell" policy as another, which the researcher says "flew through" Congress despite Democrats' concern it wasn't going to make it. The current splintering of the Democratic Party in the face the flawed rollout of the Affordable Care Act is evidence of the liberal tendency to dislike stereotypes, Stern says. Democrats lack a leader that could, hypothetically, keep them on message like conservative figures do for their group.

But Republicans' collective thinking can, in some cases, backfire. Take last year's presidential election. "There was this tendency to think, among Republicans, that there was a lot of support for [Mitt] Romney, but then the night of the election, that illusory consensus was shattered," Stern says. Perhaps there is no better example of that than what happened immediately after Fox News called Ohio—and subsequently, the election—for President Obama. Republican political consultant Karl Rove, convinced Romney would win, refused to accept the results, repeating voting numbers he'd crunched that indicated the election was too early to call. Eventually, a baffled Megyn Kelly asked a rambling Rove, "Is this just math that you do as a Republican to make yourself feel better, or is this real?"

By overestimating support, Republicans may get things done, but they can trap themselves in an ideological bubble, further inflating the popularity of conservative views. That environment, as evidenced by the Rove incident, can come crashing down when their perception of support is wrong.

As for moderates, Stern says they tend to conform unless they feel strongly motivated to deviate from the middle on a given issue. They believe there are lots more moderates like themselves out there, tending to overestimate the commonality of their beliefs.

When it comes to legislating, consensus is crucial for social change. Reaching it, however, doesn't always mean things will go as planned.

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