Playing With Different Dice

[Nightharrow]

Originally Posted by AlexanderHowl

One problem with 2d10 versus 3d6 is that the probabilities are off when translating GURPS. The average roll for 2d10 is 11, meaning a 55% chance at failure for someone with a '10'. The average roll for 3d6 is 10.5, meaning a 50% chance of failure for someone with a '10'. 3- and 18+ are much more common as well (3% chance for 3- rather than a 0.5% chance and 6% chances for a 18+ rather than a 0.5% chance).

That's a good point. I think our plan is just to give a one time bonus ~40pts so that the effective power level doesn't go down much. We will also be allowing additional levels of active defense and base attributes to make up for it. This should create a bit more of a separation from primary and secondary skills/abilities that we find desirable. The extremes we actually find more desirable, so that ends up being more of a feature than a problem.

[Nightharrow]

Originally Posted by ericthered

You'll want to expand the range of character scores, but I think that's part of your goal.



Things where 2d10 will work fairly simply:

• Skill rolls
• Attribute rolls
• Reaction rolls

Things where 2d10 will technically work but you may not want to for other reasons:

• Hit location tables
• Other 3d6 tables (mostly related to tech and magic)

Numbers whose positions you'll want to adjust:

• Self-control rolls
• Malfunction scores
• The rule of 16 (or 14).
• Critical Hit ranges

And of course damage isn't really based on 3d6 in the first place.

Thanks for the reply, this was helpful to make sure we covered major areas. It's funny you mention the rule of 16, that was actually one of our motivations for changing over. I haven't really played any supers but high level fantasy has some of the same problems. I'm not sure how to work out the probabilities when comparing different point swings for apposed rolls of high skilled (besides of course a series of sums that I don't want to do), but considering the simplified cases it seems clear a 6 point swing is pretty hard to overcome. This seems fine at first with a 16 vs 10 but when you consider an 18 vs a 24 skill it makes less sense that it is so unlikely. And this is not even at that high of a point level, it gets worse the higher you go.

[Nightharrow]

Originally Posted by Anaraxes

Or just develop a feel through play -- which is the closest to the character's actual perceptions. Outside of a few fictional characters, half of whom are making jokes, not many adventurers sit around calculating whether they've got a 37% or 48% chance of success. (They're much more likely to snap "Never tell me the odds" and blow a hero point if they have to...) It doesn't take long to develop the sense that a 6 is hard to beat, a 10 is fifty-fifty, and 13 is getting pretty likely.

Having a consistent change in probability for a particular modifier regardless of skill or circumstances is actually a detriment to verisimilitude. A novice will benefit from a small "+1" aid much more than an expert. And a little push helps change the outcome a lot more when things are balanced than when they're already askew and toppling. That same small nudge isn't then nearly as likely to make things come out your way -- you need to round up a lot of help. If you have a flat result from the die roll, then to get that effect you have to modify the modifiers on the fly, listing them all in a 2D table or run then through some formula to give the total diminishing returns. Rolling a bell curve means you can use flat modifiers while the result curve automatically adjusts how significant that +1 actually is.

I think you might be taking for granted the information you already know. Intuition can be helpful, but many things, including probabilities/statistics, are not actually intuitive unless you have studied them at length. And even then, many mathematicians hesitate before going with their intuition. The most obvious case being the Monty Hall problem, also the probability of two people in a room having the same birthday, etc...

Just to offer a different take on who may be playing... My group has 4 engineers in it, 3 of which have doctorates. A couple of them independently worked out the heat transfer of lava in a cave they where in "just to see if it was possible" because they where curious. None of these girls and guys are "winging it" not knowing the probability of a positive outcome. A couple of the others in the group can barely use a computer (I am not being hyperbolic), much less come to some sort of intuition on probabilities from rolling a few dice a hundred times over the course of weeks (nor do I think anyone could). I dont mean to be argumentative, I appreciate your post, just wanted to give a different perspective. It can just be easy to begin thinking everyone sees the world the same way we do.

It's interesting you mentioned the bell curve. From my understanding there are actually many things related to skill that do not follow the bell curve. Job performance being one that comes to mind. I think this might again be a place where intuition isn't entirely accurate. On this last point though, I admittedly have not looked up research papers on myself, Im going off of second hand reports.

Anyways, thanks for your input!

[johndallman]

Originally Posted by Nightharrow

And even then, many mathematicians hesitate before going with their intuition.

IME, what mathematicians are doing when they hesitate is working out a rough answer.

[ericthered]

The rule of 16 is probably best made into the rule of 18, 19, or 20.

I'm curious what critical hit scheme you plan to use?
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On the subject of 3d6 probabilities, I just work with the following numbers:

10 is 50% hit.
+/-2 from 10 is a 25/75 split
+/-4 from 10 is a 10/90 split

so 50, 25, and 10 are the main numbers I remember. They are simple enough. If you want to extend it to include 5/95 for 16 and 4, you can, but its rare enough that I rarely bother, and I had to look up what the numbers were.