How to win rock paper scissors revealed by scientists

When playing the famous game of rock paper scissors, people tend to let emotions get in the way and stop acting rationally, a study suggests.

Quick guide to Rock-Paper-Scissors

According to the study's authors, the game of rock-paper-scissors "serves as an important paradigm for assessing the degree of rational decision making inherent within non-cooperative environments across species".

It has been used by economists to illustrate strategic behaviours in settings where there is little collaboration.

However, for most individuals, it is a simple and fun strategic game they can play anywhere. The idea is simple: all items are equal. Paper wins over rock which wins over scissors which wins over paper.

During each round, players select one of the items in the hope of winning enough rounds to secure victory.

Published in the journal Scientific Reports, the research looks at how players act during a game when they are confronted to a computer opponent.

The scientists discovered that, even when participants had a good strategy at the beginning, the outcome of each round would make them change their behaviour. They started acting erratically.

Analysing players' response at different stages of the game, the researchers find that they follow what they call a "win-stay lose-shift' strategy. This means they would repeat the same item as long as they kept winning against the computer.

If they lost or if they were in a draw, they would change item for their next move. Surprisingly, the negative experience of losing would make them more likely to go for a downgrade. For example, if the lost with rock, they would go for scissors, the item destroyed by rock.

On the contrary, if they were in a draw with the computer, the probability of "upgrading" on the next round was higher.

Players seem to over-select "rock". Getty Images

Your best chance to win

So which strategy is effective in order to win the game every time?

Because all items carry the same weight, defeating one but losing to the other, the scientists point out that the only purely rational decision is to use each item an equal number of time, at random. This is exactly what the computer opponent was programmed to do.

However, in this particular study, the participants appeared to over-select the rock. Because paper defeats rock, over-selecting paper could have been, at least in that setting, a pathway to victory.

Since the study illuminates the processes involved in decision-making in non-cooperative environments, scientists worry about the implications in other contexts. They believe irrational individual behaviours could be common in the economic and politics field were the same non-cooperative rules apply.