Sep 11, 2009
Special thanks to listener Bill Roberston who sent in the following details about our rating system and how the re-rolls really stack up.
No, I'm not a math nerd. I was forced to
take statistics in school,
and that included a healthy dose of probability. The first part of
most probability courses covers the binomial distribution, which tells
you if you try something a bunch of times, what are the odds that 1
try will succeed, or 2 will succeed etc...
My little gamer mind immediately latched on to this, and only this,
part of the course!
For example, if I want to know the chance of a 3+ with a reroll. I
first start with a google search for binomial calculator. Next, plug
in 2 tries with a .67 success chance. Calculate the result and ask it
to tell me the chance of getting 1 or more successes.
So out of curiosity, I used the web calculator to figure out all of
the d6 with a reroll values and ranked them together with the
single-roll odds. This is the one I used.
2++ = 97%
3++ = 89%
2+ = 83%
4++ = 75%
3+ = 67%
5++ = 56%
4+ = 50%
5+ = 34%
6++ = 31%
6+ = 17%
+ = w/o a reroll
++ = with a reroll
I don't use it very much, but its very handy when coming up with house
rules to see what the effect of multiple rolls would be. Or, if I
feel like a baby, I use it to see how fast animosity will screw my Orc
army as it gets larger.