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'Rock-Paper-Scissors' study reveals humans make irrational decisions after a loss

Through studying the children’s game ‘Rock-Paper-Scissors’, research from the University of Sussex has found that people tend to make more irrational decisions following a loss.

The popular playground game has unlocked findings about human behaviour which may have significant implications for more serious situations. 

Dr Ben Dyson, Lecturer in Psychology at the University of Sussex, who led the study, explained the implications of this finding: “It’s worrying that people tended to make more irrational decisions following a loss. This could have more serious implications in higher-stake scenarios where people are competing to outmanoeuvre one another – in economics or politics, for example.

“These irrational decisions are driven by an emotional reaction to a negative outcome and leaves people vulnerable to a smart opponent.

“Emotion might have some distracting effect that deteriorates the quality of our thought. If we can learn to separate emotion from outcome, like successful Poker players, we might be able to mitigate this risk.”

The study found that Rock-Paper-Scissors is perfect for gaining critical insights into human rationality because there is no single strategy that guarantees success. Each of the three items carries equal status and therefore the rational thing to do is pick each one an equal number of times. Any deviation from this is irrational.

Human players were pitted against a computer, which was programmed to follow the ‘rational’ strategy (although participants were not told of the computer’s strategy).

They study also found that participants tended to employ a ‘win-stay, lose-shift’ strategy in playing the game. That means that when they won a round they tended to repeat the winning action but when they lost they tended to change their action.

An example of the ‘win-stay, lose-shift’ strategy where a player chooses rock in the first game:

•             If that player lost, they tended to ‘downgrade’ their item; that is to choose the item that would have been beaten by their previous choice (so, switching rock for scissors).

•             If they drew, however, they tended to ‘upgrade’ by choosing the item that would have beaten their previous choice (switching rock for paper).

•             If they won, there was a tendency to stick with the winning item (rock).

This ‘win-stay, lose-shift’ strategy is problematic in evolutionary terms because it places us in a potentially exploitable position.  It has also previously been observed in monkeys.

In this study the stakes were low - there was no additional consequence to winning, losing or drawing.

Dr Dyson adds: “If we bring money into the equation, we expect that the irrational behaviour would be accentuated. There is some evidence to back this up. The phenomenon of ‘tilting’ in Poker sees players make similarly ‘bad’ decisions on subsequent rounds following monetary loss.”

Notes to editors

“Negative outcomes evoke cyclic irrational decisions in Rock, Paper, Scissors” is published in the journal Scientific Reports.

Dr Dyson was the Principle Investigator working with graduate and undergraduate students at Ryerson University in Canada.

For more information, contact the University of Sussex media relations team: Anna Ford, Jacqui Bealing, James Hakner or Lynsey Ford. T + (0)1273 678888,

By: Anna Ford
Last updated: Thursday, 17 March 2016