Tuesday, 28 February 2017

Swift d12 Revised Probabilities

Last month I posted the probabilities for Swift d12. Since then I've streamlined the critical success system, so that a double success and 13+ are now both treated as a critical success. I was recently asked what impact this has on the probabilities, and the answer is "not too much".

This is the old approach, where a critical success required succeeding on both dice:
-5: 16.0% (0.7% critical)
-4: 30.6% (2.8% critical)
-3: 43.8% (6.3% critical)
-2: 55.6% (11.1% critical)
-1: 66.0% (17.4% critical)
+0: 75.0% (25.0% critical)
+1: 82.6% (34.0% critical)
+2: 88.9% (44.4% critical)
+3: 93.8% (56.3% critical)
+4: 97.2% (69.4% critical)
+5: 99.3% (84.0% critical)
This is the new approach, where a critical success required either succeeding on both dice or rolling 13+ on one of them:
-5: 16.0% (0.7% critical)
-4: 30.6% (2.8% critical)
-3: 43.8% (6.3% critical)
-2: 55.6% (11.1% critical)
-1: 66.0% (17.4% critical)
+0: 75.0% (25.0% critical)
+1: 82.6% (41.0% critical)
+2: 88.9% (55.6% critical)
+3: 93.8% (68.8% critical)
+4: 97.2% (80.6% critical)
+5: 99.3% (91.0% critical)
As you can see, this change increases the chance of a critical success if you already have an advantage (i.e., a bonus to the ability check). It also means that a Minion now has a chance of a critical success if they have an advantage.

Overall it's not a major difference, but it does help keep the rules a bit more consistent when there aren't too different types of critical success to get your head around.