[Afflictions] self control reduction

[Christopher R. Rice]

So the highest point value of a disadvantage with a self-control modifier is -15 (I think), a 15 or less halves the value, 12 or less is the listed value, 9 or less is 1.5 times value, and 6 or less doubles it.

That says to me that each +3 to self control is worth about 15 points. Thus each +1 to self control is worth 5 points. So for an affliction that would give you a +50% modifier (advantages are worth +10% per point since this is worth 5 points per +1 it's worth +50%). For -1 to self control rolls, use the same logic, except that it would be like afflicting a disadvantage, so +5% per -1.

But that would be for a single disadvantage you'd specify. Something like "Affliction 1 (Self Control Rolls +3, Lecherousness, +150%) [25]" So, to get around that I'd apply a multiplier of around x5. Thus each +1 to Self Control rolls is worth +250% and works on all disadvantages, while each -1 to Self Control rolls is worth +25%.

Where did I get the number? I poked at GURPS Power-Ups 4: Enhancements (p. 5) and the rules for Variable Enhancements. If we figure out how many disadvantages there are with self-control rolls (40) and map it against how many disadvantages there are total in the Basic Set (227) then we get a good percentage for calculating the value of an Accessibility: 0.1762114537. Rounding that to 18% we get a limitation value of -35%. But that's too low. Looking at the values for Trait-Limited limitations for Modular Abilities (GURPS Powers, p. 64) we see that Modular Abilities that only work for something as narrow as Languages is worth -50%. That's much closer. Thus "Variable Enhancement (Accessibility, Only Negated Advantage for disadvantages with Self-Control rolls, -50%)" is worth +50% per point of enhancements you can add. Since +1 to self control rolls is worth 5 points that gives us a value of +250% or 5x the value above.

I'm sure that new books adding new traits could be counted, but the Basic Set is a good guideline to use and less fussy.

TL;DR Each +1 to a specific disadvantage's self-control rolls is worth +50%, while each -1 is worth +5%. Multiply these values by five if it works on all disadvantages.