Taking Advantage Of Bias In Rock Paper Scissors

Here’s an infographic on how to improve you’re odds in Rock Paper Scissors. A year ago I linked to some research on bias in a coin toss (it’s not 50-50 it’s 51-49). At this rate I’ll eventually have an advantage in every game of chance.

Essentially this time around it’s more about psychology than bias in the implementation.

What’s the best way to prevent being gamed? Play rock, paper, scissor, lizard, spock, which has more possibilities and is just overall more enjoyable.

Very interesting stuff.

Coin Tosses Not Totally Random

It’s generally assumed that a coin toss is “fair” because it’s considered “random” as long as you don’t use a double headed coin. In fact professional sports like football use it. While previously known or at least suspected, it’s not so random. Research shows it has a 1% bias. Making the odds 51-49, hopefully in my favor. They were even able to build a machine to predictably flip a coin.

James Devlin at Coding The Wheel has a great writeup simplified for those who don’t have a head for all the math (pun intended):

  1. If the coin is tossed and caught, it has about a 51% chance of landing on the same face it was launched. (If it starts out as heads, there’s a 51% chance it will end as heads).
  2. If the coin is spun, rather than tossed, it can have a much-larger-than-50% chance of ending with the heavier side down. Spun coins can exhibit “huge bias” (some spun coins will fall tails-up 80% of the time).
  3. If the coin is tossed and allowed to clatter to the floor, this probably adds randomness.
  4. If the coin is tossed and allowed to clatter to the floor where it spins, as will sometimes happen, the above spinning bias probably comes into play.
  5. A coin will land on its edge around 1 in 6000 throws, creating a flipistic singularity.
  6. The same initial coin-flipping conditions produce the same coin flip result. That is, there’s a certain amount of determinism to the coin flip.
  7. A more robust coin toss (more revolutions) decreases the bias.

There’s also some potential strategy, a worthwhile read.

There paper is also available as as well if your so inclined, though you’d need to be a real math/stats nerd to want to read that.