In the research, by Yale law professor Dan Kahan, he gave identical numerical data supposedly coming from an actual survey to a sample of over 1000 people. In one of the sets of data it was described as testing skin cream effectiveness. In the other, it was testing the effectiveness of bans on concealed gun permits.
In each case the exact same numbers were given in two different ways, one that showed improved results, and one that showed lack of improvement.
But here is how Chris Mooney described the results in a Mother Jones article:
"So how did people fare on the handgun version of the problem? They performed quite differently than on the skin cream version, and strong political patterns emerged in the results—especially among people who are good at mathematical reasoning. Most strikingly, highly numerate liberal Democrats did almost perfectly when the right answer was that the concealed weapons ban does indeed work to decrease crime (version C of the experiment)—an outcome that favors their pro-gun-control predilections. But they did much worse when the correct answer was that crime increases in cities that enact the ban (version D of the experiment).
The opposite was true for highly numerate conservative Republicans: They did just great when the right answer was that the ban didn't work (version D), but poorly when the right answer was that it did (version C).
A graph of the results given in the article may raise questions about the "numeracy" classifications, or perhaps liberals only develop bias above numeracy level 5.5 while conservatives bias runs across a wider range of ability. But they clearly support the idea that they gave the answer they wanted, rather than the one they surely knew to be true.
Moody concluded with a telling statement, "The Scottish Enlightenment philosopher David Hume famously described reason as a "slave of the passions." Today's political scientists and political psychologists, like Kahan, are now affirming Hume's statement with reams of new data. This new study is just one out of many in this respect, but it provides perhaps the most striking demonstration yet of just how motivated, just how biased, reasoning can be—especially about politics."