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If these studies aren’t sobering enough, consider this one, described by one magazine as “The Most Depressing Discovery About the Brain, Ever.”28 Kahan recruited a thousand Americans from all walks of life, assessed their politics and numeracy with standard questionnaires, and asked them to look at some data to evaluate the effectiveness of a new treatment for an ailment. The respondents were told that they had to pay close attention to the numbers, because the treatment was not expected to work a hundred percent of the time and might even make things worse, while sometimes the ailment got better on its own, without any treatment. The numbers had been jiggered so that one answer popped out (the treatment worked, because a larger number of treated people showed an improvement) but the other answer was correct (the treatment didn’t work, because a smaller proportion of the treated people showed an improvement). The knee-jerk answer could be overridden by a smidgen of mental math, namely eyeballing the ratios. In one version, the respondents were told that the ailment was a rash and the treatment was a skin cream. Here are the numbers they were shown: Improved Got Worse Treatment 223 75 No Treatment 107 21 The data implied that the skin cream did more harm than good: the people who used it improved at a ratio of around three to one, while those not using it improved at a ratio of around five to one. (With half the respondents, the rows were flipped, implying that the skin cream did work.) The more innumerate respondents were seduced by the larger absolute number of treated people who got better (223 versus 107) and picked the wrong answer. The highly numerate respondents zoomed in on the difference between the two ratios (3:1 versus 5:1) and picked the right one. The numerate respondents, of course, were not biased for or against skin cream: whichever way the data went, they spotted the difference. And contrary to liberal Democrats’ and conservative Republicans’ worst suspicions about each other’s intelligence, neither faction did substantially better than the other. But all this changed in a version of the experiment in which the treatment was switched from boring skin cream to incendiary gun control (a law banning citizens from carrying concealed handguns in public), and the outcome was switched from rashes to crime rates. Now the highly numerate respondents diverged from each other according to their politics. When the data suggested that the gun-control measure lowered crime, all the liberal numerates spotted it, and most of the conservative numerates missed it—they did a bit better than the conservative innumerates, but were still wrong more often than they were right. When the data showed that gun control increased crime, this time most of the conservative numerates spotted it, but the liberal numerates missed it; in fact, they did no better than the liberal innumerates. So we can’t blame human irrationality on our lizard brains: it was the sophisticated respondents who were most blinded by their politics. As two other magazines summarized the results: “Science Confirms: Politics Wrecks Your Ability to Do Math” and “How Politics Makes Us Stupid.”29