Friday, May 28, 2010

What's the probability?

That is one of my most common questions. I very often wonder just that. What's the probability of something happening? I'd like to tell before rolling dice about probabilities. I one took down the math books for some basic high school mathematics, and even though I had once studied that I couldn't make head or tail out of it. 

I have posted about my Wednesday game before, and the great fun of playing 3:16. One reason it have been fun is that one of my players, who usually don't complain about dice or luck, in the session last week rolled amazingly bad!

Imagine rolling 20-something d20 rolls a night, and having 14 of those turn up a 0!

That guy missed a lot, but when he managed to roll under 8 for his Fighting Ability check, his kill number were impressive. His ability to roll high was consistent. In a game system where you should roll low, but higher than the opposition, his rolls where hilarious. Of course I had him narrate all his failures.

But, what's the probability?

Apparently poker buffs don't talk about luck, they talk about "variance". The same guy who rolled all those zeroes told me, that some have kept statistics on all their hands to calculate "variance". Even though it should even out, they have decided that there seem to be such a thing as luck. Everything should even out, eventually, right? The question is how close to infinity you have to get.

But, rolling 14 0 out of 20 something rolls? What's the probability of that happening? Amazing. I love dice.


  1. The better question is "What are the odds of something noticeable happening?" Given that you play a lot and there are a lot of trends you would find remarkable if they happened, quite high. The face on Mars would be equally remarkable if it appeared to be a hand, a cat, a swastika ... I wonder if the Martians marvel at the "boot on Earth"?

  2. Well, at least humans love to find patterns and meanings in things, right? :)

  3. Well, the probability of getting 14 of a kind with 20 dice is:

    3.478x10^-13 ~~ 1 in 2875176721172

    I cheated and used wolframalpha:

  4. Hey, you should know how to cheat. It's a survival skill. :)

  5. Of course, most dice are biased to fall a particular way, so it would be slightly more likely to happen!

  6. Don't we all use precision dice? :)


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