How to win rock-paper-scissors (almost) every time


(Gordon Cranford/Flickr)

Rock-paper-scissors is a schoolyard game/universal bar-tab-settler that theoretically relies on chance. After all, each person in the game plays one of three hands at random each time. Right?

Wrong! Scientists at China’s Zhejiang University just released the results of the first large-scale study of the game — and they found that player behavior typically follows a predictable pattern. It goes something like this:

People start by picking each variable (rock, paper or scissors) about one-third of the time. You can’t really game this stage. BUT after the first round:

  • If a player wins, he will usually stick with the same play.
  • If a player loses, he will usually switch actions in “a clockwise direction”: rock changes to paper, paper to scissors, scissors to rock.

This is simple, but a little hard to envision — so let’s try an example. Say I am playing three rounds of rock-paper-scissors with my cubemate Emily.

Round 1: Emily plays paper, I play rock. She wins.
Round 2: Emily plays paper, I switch to paper. We draw.
Round 3: Emily plays scissors, I switch to scissors. Another draw! I lose.

But if I had kept the probabilities from this Zhejiang University study in mind, I could have changed my gameplay like so:

Round 1: Emily plays paper, I play rock. She wins.
Round 2: Emily plays paper, I switch to scissors. I win.
Round 3: Emily switches to scissors, I switch to rock. I win again!

You can thank game theory for your improved rock-paper-scissors game. Researchers previously believed the game operated according to a game theory tenet called “the Nash equilibrium” — basically, the idea that people will chose each of the three options equally over time. But studied on a larger scale, it appears play follows a cyclical pattern — which means sneaky players can use “conditional response,” a reaction to a specific stimulus, in order to optimize their records.

That has fascinating implications not only for your next bet, but for human psychology.

“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,” the Zhejiang researchers conclude.

Almost as challenging as losing a rock-paper-scissors game now … amirite?


Caitlin Dewey runs The Intersect blog, writing about digital and Internet culture. Before joining the Post, she was an associate online editor at Kiplinger’s Personal Finance.
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