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George F Quail

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02:35 pm: oWoD Dice Probabilities
This blog post is an interesting little set of tables on the Old World of Darkness system on how likely you are to succeed or fail based on starting dice and target number. In WoD you roll a certain amount of D10s and are trying to get at least one of them equal or above the target number:. It's written from the point of view of Street Fighter: The Storytelling Game but the basically maths work out across the system.

While it would be unfair to say I'm a huge fan of the nWoD system, I do think the system is flat-out superior to the oWoD one. One reason for that is the subtraction of "1s" from successes in the dice pool and Botch rule, where having too many 1s generates spectacular failures. As with most such systems the idea is to produce a rule that mimics the enormously dangerous failures which occur when people get things seriously wrong.

As well as the usual problems with critical failure systems - that randomly generated failures will come up more for players since they roll more dice than any one NPC - this system also annoyed me because it generated an extra operation in dice rolling. "Did I get at least one dice roll above the target number? Yay!.... Oh, wait, now I must subtract any ones I rolled". it also produces the feeling that the more dice you roll, the more likely you are to see 1s somewhere in the pool - and thusly it can almost feels like the system is punishing you for having lots of dice.

These tables indicate that probability backs up my impression of the system. Even with a large pool of dice, botches are likely - Difficulty 8 is pretty hard, yes, but even on 9 dice you have about a 10% chance of comically making things worse. The phenomenon is more pronounced at difficulty 9, where your chance of botching gets higher the more dice you add to your pool until you reach difficuly 6 - so while failure is more likely, you the player may be safer if you roll less dice. (Obviously a GM can try to make sense of these numbers, but how would you resovle failing to climb and botching a climb? If botching is falling off and hurting yourself, people with less climb skill are less likely to do that.)

nWoD removes the whole "1s subtract" thing and mostly sticks to a single target number of 8 throughout. It also requires just one success for almost all actions, whereas lower difficulty numbers but multiple required successes were more common before. This does mean a GM loses a lot of leeway in difficulty setting.... but it also removes a lot of the statistical weirdness shown in those tables.

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