The feeling that's worse than dread? Uncertainty: It may be better to keep people blissfully ignorant rather than telling them there is a chance of bad news 

It may be better to keep people blissfully ignorant rather than telling them there is a chance of bad news, a study suggests.

This is because uncertainty is more stressful than knowing something bad will definitely happen, a study found.

Pessimists may seize on the findings as proof it is right to look on the gloomy side of life after all.

People told that they had a chance of getting a painful electric shock found that more stressful than being told they would definitely receive it.

Uncertainty is more stressful than knowing something bad will definitely happen, a study by the University College London found. Pessimists may seize on the findings as proof it is right to look on the gloomy side of life

University College London researchers created an experiment where people were told they had either no chance of receiving a shock, a 50 per cent chance or that they would definitely get a shock.

The study published in Nature Communications, found that people who had a 50% chance of receiving a shock were under the most stress, while those expecting a zero per cent chance, or 100 per cent chance were the least stressful.

To test the theory, the experiment involved 45 volunteers who played a computer game in which they turned over rocks that might have snakes under them.

They had to guess whether or not there would be a snake, and when there was they received a mildly painful electric shock on the hand.

Over time they learned which rocks were most likely to harbour snakes, but those odds changed throughout the experiment, generating fluctuating levels of uncertainty.

Lead author Archy de Berker of the UCL Institute of Neurology said: 'Using our model we could predict how stressed our subjects would be not just from whether they got shocks but how much uncertainty they had about those shocks.

People told that they had a chance of getting a painful electric shock found that more stressful than being told they would definitely receive it (file photo)

'Our experiment allows us to draw conclusions about the effect of uncertainty on stress. It turns out that it's much worse not knowing you are going to get a shock than knowing you definitely will or won't. We saw exactly the same effects in our physiological measures - people sweat more and their pupils get bigger when they are more uncertain.'

The researchers said that this is the first time that the effect of uncertainty on stress has been quantified, but the concept is likely to be familiar to many people.

Co-author Dr Robb Rutledge of UCL added: 'When applying for a job, you'll probably feel more relaxed if you think it's a long shot or if you're confident that it's in the bag.

'The most stressful scenario is when you really don't know. It's the uncertainty that makes us anxious. The same is likely to apply in many familiar situations, whether it's waiting for medical results or information on train delays.'

While stress is often seen as negative in modern society, the study found that people whose stress responses spiked the most at periods of greatest uncertainty were better at judging whether or not individual rocks would have snakes under them.

Dr Sven Bestmann of UCL said: 'From an evolutionary perspective, our finding that stress responses are tuned to environmental uncertainty suggests that it may have offered some survival benefit.'

'Appropriate stress responses might be useful for learning about uncertain, dangerous things in the environment. Modern life comes with many potential sources of uncertainty and stress, but it has also introduced ways of addressing them.

'For example, taxi apps that show where a car is can offer peace of mind by reducing the uncertainty about when it will arrive. 

'Real-time information boards at bus stops and train platforms perform a similar role, although this can be undermined by unspecified delays which cause stress for passengers and staff alike.'