Sunday, August 21, 2011
d20 vs. 3d6 Attribute Checks
For example, if I have a 14 strength, pretty good, and have to roll 14 or under on a d20, that's 14 chances in 20, or a 70% chance of success.
If I am a weak little fellow with a STR of 6, my 6 chances in 20 = 30% success rate.
STR 11 = 55% success rate on a d20 attribute check, and STR 18 = 90% success rate on a d20 attribute check.
Got it. Pretty reasonable-seeming mechanic.
But while I understand the concept of the bell curve and know that the results of several 3d6 rolls average out toward the middle of the range over successive rolls, I cannot quite conceive how that impacts the chances for a STR 18 attribute check vs. a STR 11 attribute check. Here is Gygax's table:
Am I correct to interpret this as meaning that a STR 11 fighter has a 13% success rate on a 3d6 attribute check, and that a STR 18 fighter has a 1% success rate? I love d6-based mechanics like 2d6 Thievery and 2d6 Bardery but this 3d6 vs. d20 attribute check thing seems kind of extreme -- like a 3d6 attribute check mechanic would be way unfair to characters with attributes in the 12-18 range.
* I'm no mathematician -- I stole everything I know about how dice generate probabilities from EGG's discussion of the topic on pp. 9-10 of the Dungeon Master's Guide.