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The scientific way to win at rock-paper-scissors

May 02, 2014

Mathematicians believe it’s possible to predict what your opponent will do.

You don’t need to be a mind reader to win at rock-paper-scissors according to a new study: just knowing a bit of maths will do.  In theory, the best way to play is to choose rock, paper or scissors completely at random. That way, your opponent can't predict what's coming next. If both players do this, then neither of them can improve their chances by trying a different strategy - a situation known as a Nash equilibrium.

But in reality, it's not so simple: playing randomly is harder than it sounds. Researchers in China who studied games of rock-paper-scissors played between 360 people found that each option was chosen a third of the time on average, as you would expect if they were picking randomly. But when they analysed each game individually they discovered players were unconsciously adopting different strategies. When someone won, they tended to stick with the same option for the next round. Losers tended to change, and usually moved through the sequence rock-paper-scissors in order. Scientists call this a ‘conditional response’, where the brain responds in a certain way to certain circumstances, and believe it could be useful in analysing human behaviour in other situations such as financial trading – where the risks and rewards are much higher.

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