Should computers make all our decisions? In a new book published today, three top scientists argue that human beings are useless at making choices. Machines would do a much better job.

But this kind of system only works if we know that the professionals are making the right decisions. Noise, a new book by Daniel Kahneman, Olivier Sibony and Cass R Sunstein, suggests that it happens far less than we might like to believe.

The authors claim that professional decisions that are supposed to be objective are actually warped by tiny, unnoticeable influences in our environment, which they call noise.

For example, a doctor might give you a different diagnosis depending on what the weather was like on the day of your appointment, or whether they had eaten breakfast that morning - or had a good night's sleep.

This noise has serious consequences for society. It means experts can end up making very different decisions in similar cases. We like to think that in a fair legal system, for instance, two people who are found guilty of the same crime will be given identical punishments. But history suggests that this is not the case.

In one study, in 1981, 208 judges were asked to hand down sentences in 16 hypothetical legal cases. They were only given the most basic details of the case so there was no room for bias.

Yet in only three of these cases did all the judges agree that a prison term was appropriate. And the average difference in prison time handed down by any two of these judges was a staggering 3.5 years.

This might not matter if we were more aware of how noise influences our decisions. But most professionals overestimate their ability to make accurate, fair judgements and so are unable to adjust their choices to account for it.

Judgement time

Kahneman, Sibony and Sunstein suggest it would ultimately be better to entrust all decisions to algorithms. Unlike human beings, computers are not affected by tiredness, weather, hunger or emotions.

That means their judgements are much less noisy. A computerised doctor could identify illnesses more accurately. An AI judge's verdicts would be perfectly consistent.

But others are wary. They point out that while human experts do make mistakes, we can hold them to account for this by appealing a legal decision or disciplining a doctor for negligence. But a computer's decision is supposedly objective - and therefore final.

And sometimes the human capacity to process environmental factors is important. A judge might feel compassion for a young offender and decide to give them a lenient sentence in the hope that this small act of kindness will persuade them to change their ways. An algorithm cannot show such empathy.

Should computers make all our decisions?

Yes, say some. Human beings are much too fallible to be trusted with important decisions. A person's life can be ruined because a judge forgets to eat their lunch, or their doctor is going through a messy divorce or because the weather has turned cloudy. Using algorithms to make decisions is the only way of ensuring fairness, consistency, and accuracy in our everyday lives.

Not at all, say others. An algorithm is only as good as the person programming it, and that person is just as susceptible to noise as any other expert. Besides, human variability is a gift, not a curse: it is what makes us creative and critical beings. And it allows us to recognise failures and injustices in our systems and work towards changing them.