Lynata wrote:That being said, given how deadly this effect can be on lower level characters and enemies, perhaps a houserule that adds a +1 bonus after each failed test would help? This way, in the 1st round of stun the test would be 9.26%, in the 2nd round 16.2%, in the 3rd 25.92% and so on...
The cumulative probability of making a TN 15 test, then a TN 14 test, then a TN 13 test is (given a +0 modifier) actually 43.7% (9.26 + 14.7 + 19.71 = 43.68)You sure you didn't accidentally use the numbers from the series without any +1 bonuses? (I.e. the 9.26, 8.40, 7.62 series making up 25.29 - I note that your 25.92 could be the same number only with two figures jumbled)
Anyway, you all might jump at the rather larger chance - 44% instead of 25%, a difference of 19 percentage units or an seventy-five percent increase - but this is because of the specific shape of the 3d6 bell curve. A +1 bonus is very valuable when the slope is steep, as it is in this case. Contrast with either the case when Constitution is not 0 but -2 or +2 instead...
Con -2 without the cumulative +1 bonus (three TN 17 tests): 1.85+1.82+1.78=5.45
Con -2 with the cumulative +1 bonus (a TN 17, a TN 16 and a TN 15 test): 1.85+4.54+8.67=15.1
The difference is 9.65 percentage units; the probability might be tripled but goes from a very low number to a slightly larger but still low number.
Con +2 without the cumulative +1 bonus (three TN 13 tests):25.93+19.20+14.23=59.36
Con +2 with the cumulative +1 bonus (a TN 13, a TN 12 and a TN 11 test):25.93+27.78+23.15=76.85
The difference is 17.5 percentage units; this is an increase by only thirty percent.
By this I only mean to say that the bonus makes a big impact on the example discussed but not necessarily as big an impact when the numbers are different. (AGE is decidedly different than D&D here - even though both games operate on roughly the same 3-18 scale a +1 bonus is always equally valuable in all D&D cases, where the utility differs greatly in AGE)
PS. For unparallelled probability calculating power, do use Troll
. This tool really stands head and shoulders above anything else in the way of dice calculators.