Why are we irrational? How a logical flaw stops us solving problems

Myths and stories trump rational reasoning when it comes to analysing distant threats like climate change. But we have tools to combat that – and it’s a myth irrationality is on the rise

By Graham Lawton

TAKE a look at the data to the right, showing crime rates in US cities according to whether or not they ban concealed handguns. Based on these numbers, would you conclude that gun control reduces crime? Take as much time as you want.

If you answered no, give yourself a pat on the back. Most people answer yes, dazzled by the large number of cities with gun control and decreasing crime. But what matters is the proportion of cities with falling crime. That’s 75 per cent for cities with gun control and 84 per cent for those without. The rational conclusion is that gun control increases crime, or at least doesn’t decrease it.

Before you punch the air or a passer-by, the data is fake. But faced with it, supporters of gun control are more likely to jump to the wrong conclusion. Opponents of gun control scrutinise the data more cautiously and more often spot the real pattern.

The test is designed to winkle out a pervasive and intractable source of human irrationality, the myside bias. It expresses the tribal thinking that evolution has gifted us (see “Why are we good and evil?”): a tendency to seek and accept evidence that supports what we already believe. “You direct your reasoning to end up with a conclusion that is already a sacred belief or a shibboleth in your side, your team, your coalition, your party, your posse,” says Steven Pinker at Harvard University, author of Rationality: What it is, why it seems scarce, why it matters.

On …