Then there’s the question of rationality – how well you can make optimal decisions, by weighing up evidence and discounting irrelevant information.

You might assume that the more intelligent you are, the more rational you are, but it’s not quite this simple. While a higher IQ correlates with skills such as numeracy, which is essential to understanding probabilities and weighing up risks, there are still many elements of rational decision making that cannot be accounted for by a lack of intelligence.

Consider the abundant literature on our cognitive biases. Something that is presented as “95% fat-free” sounds healthier than “5% fat”, for instance – a phenomenon known as the framing bias. It is now clear that a high IQ does little to help you avoid this kind of flaw, meaning that even the smartest people can be swayed by misleading messages.

People with high IQs are also just as susceptible to the confirmation bias – our tendency to only consider the information that supports our pre-existing opinions, while ignoring facts that might contradict our views. That’s a serious issue when we start talking about things like politics.

Nor can a high IQ protect you from the sunk cost bias – the tendency to throw more resources into a failing project, even if it would be better to cut your losses – a serious issue in any business. (This was, famously, the bias that led the British and French governments to continue funding Concorde planes, despite increasing evidence that it would be a commercial disaster.)

Highly intelligent people are also not much better at tests of “temporal discounting”, which require you to forgo short-term gains for greater long-term benefits. That’s essential, if you want to ensure your comfort for the future.

Besides a resistance to these kinds of biases, there are also more general critical thinking skills – such as the capacity to challenge your assumptions, identify missing information, and look for alternative explanations for events before drawing conclusions. These are crucial to good thinking, but they do not correlate very strongly with IQ, and do not necessarily come with higher education. One study in the USA found almost no improvement in critical thinking throughout many people’s degrees.

Given these looser correlations, it would make sense that the rise in IQs has not been accompanied by a similarly miraculous improvement in all kinds of decision making.

As I explain in my book on the subject, a lack of rationality and critical thinking can explain why financial fraud is still commonplace, and the reason that millions of people dish out money on quack medicines or take unnecessary health risks.

For our society, it can lead to medical errors and miscarriages of justice. It may have even contributed to disasters like the Deepwater Horizon oil spill and global financial crises. It is also contributing to the spread of fake news, and the huge political polarisation on issues like climate change – preventing us from finding an agreed solution before it is too late.