How to win at rock-paper-scissors

What are your odds of winning rock-paper-scissors? Simple – one in three. At least, that’s what chance predicts. But people do not play randomly – they follow hidden patterns that you can predict to win more games than you should, a study has revealed. Winners tend to stick with their winning action, while losers tend to switch to the next action in the sequence “rock-paper-scissors”. Anticipating these moves could give you a winning edge, say scientists.

Their strategy was revealed in a massive rock-paper-scissors tournament at Zhejiang University in China, documented on the Arxiv server. Scientists recruited 360 students and divided them into groups of six. 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.

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). 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. Edited from How to win at rock-paper-scissors.

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