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Increase your odds

Rock-paper-scissors
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Next time you take on a rock-paper-scissors challenge, you might like to consider the science available to increase your chances of winning.

A new study has revealed your chances of winning increase from three-in-one if you consider human psychology at play.

Winners tend to stick with their winning action, while losers tend to switch to the next action in the sequence “rock-paper-scissors”, reports the BBC, quoting the results of the stidy.

The scientific strategy was revealed in a rock-paper-scissors tournament at Zhejiang University in China which was then tested by scientists using 360 subjects divided into groups of six.

In the study, each competitor played 300 rounds of rock-paper-scissors against other members of their group.

As an incentive, the winners were paid – in proportion to their number of victories.

To play smart, classical game theory suggests players should completely randomise their choices – to remain unpredictable and not be anticipated by opponents.

This pattern – where both players select rock, paper or scissors with equal probability in each round – is known as the Nash equilibrium.

The strategy is named after game theory pioneer John Forbes Nash Jr, subject of the 2001 Hollywood film A Beautiful Mind, which starred our own Russell Crowe.

And indeed – in the Chinese tournament players in all groups chose each action about a third of the time, exactly as expected if their choices were random.

However, on closer inspection, the organisers noticed a surprising pattern of behaviour.

When players won a round, they tended to repeat their winning rock, paper or scissors more often than would be expected at random (one in three).

The study found losers, on the other hand, tended to switch to a different action. And they did so in order of the name of the game – moving from rock, to paper, to scissors.

After losing with a rock, for example, a player was more likely to play paper in the next round than the “one in three” rule would predict.

This “win-stay lose-shift” strategy is known in game theory as a conditional response – and it may be hard-wired into the human brain, the researchers say.

Anticipating this pattern – and thereby trumping your opponent – “may offer higher pay-offs to individual players” they write.

“The game of rock-paper-scissors exhibits collective cyclic motions which cannot be understood by the Nash equilibrium concept.

“Whether conditional response is a basic decision-making mechanism of the human brain or just a consequence of more fundamental neural mechanisms is a challenging question for future studies.”

Though it is only a simple game, rock-paper-scissors is seen as a useful model for studying competitive behaviour in humans – in financial trading for example.