It’s worth getting all the facts before making a decision muharrem öner/getty

People jump to conclusions they want to be true, even when it is against their interests to do so, according to a study of how we make decisions.

“In the case of topics important for one’s identity, preferential treatment of information consistent with a person’s worldview is understandable,” says Filip Gęsiarz of University College London. “It can fulfil many psychological needs other than a search for objective truth, such as protecting one’s core values or avoiding uncertainty.”

So when it comes to big, defining issues such as Brexit or climate change, we know that objective truth isn’t always what people are looking for. But Gęsiarz and his colleagues wanted to see whether similar factors were involved even in trivial judgements, and ones where it pays to be accurate.


They ran an experiment in which participants had to draw conclusions by gathering data over time. People were asked to watch a screen depicting a factory conveyor belt carrying TVs and phones, and then decide which type of device the factory mainly produced.

In some factories, 60 per cent of the devices were TVs and 40 per cent phones, while in others the ratio was the opposite. The 84 participants were allowed to choose when they had enough evidence to make up their minds, and they were given a monetary reward for correct decisions.

However, they were also randomly allocated into one of two groups: one received a cash bonus each time a factory that primarily produced TVs came on screen and the other received the bonus for phone factories. They got this bonus regardless of whether they correctly identified the factory as a phone or TV producer.

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This meant that one type of factory was clearly preferable, but the only way participants could maximise their rewards was to accurately identify the type of factory, as they had no control over which would come on screen.

“It turned out that it was enough to induce a whole range of biases in how people gathered information,” says Gęsiarz. “They were deciding that there were more phones on the conveyor belt more often, upon seeing less evidence and required less consistent evidence to do so.”

Gęsiarz says two different biases were driving this behaviour: a tendency to believe in favourable conclusions before seeing any evidence, and weighing evidence that was consistent with a favourable belief more strongly.

“Although these findings are consistent with what we know about confirmation biases, we were still surprised that most participants were prone to them in a situation where it is much more clear that having a bias might be self-defeating,” says Gęsiarz.

But he says there are things we can do to improve the way we gather information. “Awareness of such biases, together with a deliberate practice of being a ‘devil’s advocate’ for our favoured beliefs might help in counteracting their influence,” says Gęsiarz.

Being curious about things we want to be true, rather than taking them at face value, could also contribute to a more accurate view of the world, he says.

David Sewell at the University of Queensland, Australia, says we should not only consider whether the evidence for our beliefs possibly supports another interpretation, but we should also take that other interpretation seriously.

Yet no matter how good we become at carefully evaluating the evidence in one particular area, whether it be in financial matters, global politics or relationships, the sheer volume of decisions we have to make each day means these cognitive biases are liable to creep in elsewhere, he says.

“It often might seem that our worldview is well-supported by the facts, often forgetting that we gather these facts in a biased manner, therefore making sure that most evidence that we’re familiar with supports our favoured conclusions,” says Gęsiarz. “While searching for information, we stop the investigation as soon as the jury leans in the desired direction.”

Journal reference: PLoS Computational Biology, DOI: 10.1371/journal.pcbi.1007089