Do the best you can until you know better. Then when you know better, do better. – Maya Angelou

Mr. Walker's Classroom Blog

Science Has Finally Figured Out How to Win Rock-Paper-Scissors

Original Article at Gizmodo

Turns out that all you rock-paper-scissors champions who chalk it up to skill over luck may be on to something. Because according to science, there might actually be a winning strategy to this greatest of metacarpal match-ups.

The bold claim comes from a collective of Chinese researchers who recently took 360 students, broke them into groups of six, and had them play 300 rounds of the game in random pairings. To make sure players never lost incentive (which would be understandable after round 30, much less 300), the winners of each round were given a small sum of money as a reward.

So what do you need to know to win? After observing the many, many rounds, the scientists found that "if a player wins over her opponent in one play, her probability of repeating the same action in the next play is considerably higher than her probabilities of shifting actions."

On the other hand, if a player loses two or more times in a row, he or she will not play the same sign, but will instead play whichever sign would have beaten the one that had just allowed his or her opponent to win. So if Player A has been on a losing streak, and Player B just threw down scissors to beat A’s paper, A will likely throw down a rock, which stands a good chance of winning since B is likely to stick with his previously won hand anyway. This is called the "win-stay, lose-shift" strategy.

Granted, all that’s a little hard to follow. So here’s a cheat sheet. For our purposes, we’ll call your opponent Chad. No one likes a Chad:

If you won the last round…
  • …by playing rock, play scissors next.
  • …by playing scissors, play paper next.
  • …by playing paper, play rock next.
If you lost the last round (and Chad hasn’t seen this study yet)…
  • …by playing rock, play scissors next
  • …by playing scissors, play paper next.
  • …by playing paper, play rock next.
If you lost the last round (and Chad has already seen this study)…
  • …by playing rock, play paper next.
  • …by playing scissors, play rock next.
  • …by playing paper, play scissors next.