Speech Formula (Fallout 3)

Pass Chance = Disposition Value * Speech Value * Difficulty Value

the final Pass Chance is based on a value between 1 and 0, if the chance is greater than fSpeechAutoSuccessThreshold then the check will always succeed.

Game settings used in the formula

Setting	Default	Description
fSpeechAutoSuccessThreshold	0.9	If the chance to pass is greater than this value, the speech check always counts as succeeded. Default of 0.9 = 90%.

Disposition Value

Although called here "disposition value", this section of the formula is the most complex and accounts for the most variables.

Disposition Value = (((Charisma Value + Karma Value) + (IsWeaponOut * fDispTargetWeaponBase) + Actor Base Disposition) - fSpeechChallengeDispositionBase) * fSpeechChallengeDispositionMultiplier / 100 + 1

Charisma Value = (Player Charisma - fDispTargetCharOffset) * fDispTargetCharMult + fDispTargetCharBase

Karma Value = (Actor Responsibility * fDispActorRespMult + fDispActorRespBase) * (Player Karma * fDispTargetKarmaMult)

Game settings used in the formula

Setting	Default	Description
fDispTargetCharOffset	5.0	Offset for player Charisma.
fDispTargetCharMult	10.0	Multiplier for player Charisma to actor disposition.
fDispTargetCharBase	0.0	Base charisma-to-disposition value.
fDispActorRespMult	1.0	Multiplier for actor responsibility value.
fDispActorRespBase	-50.0	Offset for actor responsibility.
fDispTargetKarmaMult	0.002	Multiplier for player karma, both good and evil actors like good karma players more.
fDispTargetWeaponBase	-10.0	Modifier to actor disposition when the player has their weapon drawn.
fSpeechChallengeDispositionBase	30.0	Used to determining the "average" disposition in actors.
fSpeechChallengeDispositionMultiplier	1.0	Multiplies the modified actor disposition by this value.

Speech Value

Speech Value = (Player Speech - fSpeechChallengeSpeechBase) * fSpeechChallengeMultiplier / 100 + 1

Game settings used in the formula

Setting	Default	Description
fSpeechChallengeSpeechBase	50.0	Offset for determining the "average" player Speech skill.
fSpeechChallengeMultiplier	2.0	Multiplier for adjusting player Speech skill when not "average".

Difficulty Value

Difficulty Value = (100 - Difficulty) / 100

Game settings used in the formula

Setting	Default	Description
iSpeechChallengeDifficultyVeryEasy	10.0	Difficulty adjustment for very easy speech checks.
iSpeechChallengeDifficultyEasy	40.0	Difficulty adjustment for easy speech checks.
iSpeechChallengeDifficultyAverage	55.0	Difficulty adjustment for average speech checks.
iSpeechChallengeDifficultyHard	70.0	Difficulty adjustment for hard speech checks.
iSpeechChallengeDifficultyVeryHard	80.0	Difficulty adjustment for very hard speech checks.