Mike's Standard Rant #5: The Myth of Opposed Rolls

[Mike Holmes]

Wart and Reimer,

I admitted to the possibility of an aesthetic argument. What you call semiotics, Reimer, was exactly what I was refering to there. You have brought the right term to bear; very good, I missed that. From that POV, Wart, you are right, this is a preference. If you are willing to put up with the admittedly small potential downsides, for something you see as being more intuitive, then that's a choice I can't refute. But there are still some points I'd like to make.

When designing, simply deciding to have a single system is not enough to make a good system. It is merely one step. Yes, while what I have displayed only argues that all methods are mathematically equal, I do so to point out that there is no "danger" from going with one system. Once you get past that assumption (and whether you agree with it or not) the next step is to create a system that is semiotically, aesthetically, and otherwise mechanically accessible. Somehow the asumption here is that I would make some kind of ridiculous system to follow on this assumption. I would not do so, nor would I suggest that anyone else do so.

Let's take a look at some systems that follow my assumption, and work very well. Sorcerer is "all opposed", and works wonderfully. As is Dunjon Krawl (and I assume Dunjon, though we've not seen it). Mithras's Zenobia is where I got on the bandwagon originally with its opposed roll combat. Interesting how many games have combat systems without opposed rolls, or strange modifications of opposed rolls, and then straight opposed rolls for everything else (see Rant #3). Inspectres is an odd case because the rolls are entirely unopposed. That is, they are based only on the character's stat, and there are no difficulties, targets, nothing. Still works. It's one exception is Stress rolls which are separated out specifically to highlight their difference. The aforementioned Scattershot. And you'll have to trust me that all my designs that use one method all work just fine. I'm sure there are other prime examples that aren't coming to mind right now, as well.

None of these systems have any problems with a lack of data (well, InSpectres does, but intentionally). You can always adjust either side of a conflict in either form by raising or lowering targets, or raising or lowering skills. In fact the reason I am partial to "all opposed" is that you get all that information in using the exact same methods for all sides present. You simply seem to be arguing right for my favorite of the two methods, Reimer.

And none of these systems is in any way incomprehensible to anyone. The active/passive dichotomy is illusionary anyhow. Is a stone falling active or passive? What if I pushed it off the edge? How are these situations different from the player's perspective? He only want's to know if he got crushed by it or not. And having only one method, he will be better able to judge his chances, not having to learn more than one way to calculate his odds.

I am not sure what you are talking about, Reimer, with respect to GURPS or D&D. They, as you point out, do have the problem of multiple systems, which you say is bad in the case of D&D (they have improved slightly in theis area, but are still amongst the worst of offenders; it makes me laugh when people describe D&D as simple). Then you point out that GURPS (which also has opposed vs unopposed rolls, and other various types to boot) should be more complicated than it is by having more types of charts. Well, I could argue against that, but the charts in question aren't even part of the resolution system, so I don't see how that's gemain. In any case, I don't see GURPS suffering from a lack of complexity. I would argue that Ars Magica suffers from its differing resolution methods, but you'd probably disagree. I do have the designers of the game on my side, however, who's later games included less and less different resolution mechanics.

The case of Falkenstien's sorcery vs. skill checks I would agree with being a good idea. But this is because, again, there is a good reason for the dichotomy. This is not the mythic opposed vs. unopposed example, which does not merit a difference, but one that does.

All I'm saying is that, assuming that you follow up with a good system, you lose nothing from going with a single system, while gaining simplicity. This is the definition of elegance. Note that I am a big fan of complexity (reference my ongoing battle with Mr. Martin over that one), as long as it provides something. But when things can be made simpler without losing anything this is obviously an advantage.

Mike

[Paganini]

First of all remember, this is an opposed-roll mechanic.  That's why it simplifies to Your Skill + d10 – d10 versus My Skill.  The subtraction is inherent and unavoidable.  Wouldn't you agree that having addition, on top of subtraction, is more "evil"?

Normally, I would, but not in this specific case. d10 - d10 can be read by inspection: take a black d10 and a white d10 (or your choice of colors) and make one the + die and the other the - die. Whichever die rolls lowest is the result, with the sign being determined by the color. This is identical to d10 - d10, but doesn't need subtraction. So, you only have subtraction if you roll a negative number - it's an either or situation.

Ah, but that would destroy the utility of the 'faux opposition roll.'

This is intriguing, but I want to make sure I really grasp it. Could you give examples of a 'faux opposition roll' and a normal roll for comparison?

If we 'flop' the dice over into positives, we have to 'reinstall' the target number and all of them would have to be calculated as Target Number + 11.  (The normative skill rating is 11, added to 2d10 makes the range from 13 to 31!  That would require target numbers centering around 22!  To me that's counter-intuitive, not only adding target numbers to the mix (beyond the Your Skill Rating), but also making them always land between 13 and 31.  Those numbers impressed me!

Hehe. Good point. :)

In the second place, if you want a system where the roll translates directly to the degree of success using modifiers to represent situational considerations, why do you want a bell curve at all? Bell curves do bad things to modifiers. Seems like it'd make more sense to roll a d20 or a d10.

How did he put that?  It was something like 'putting a high-power scope on your rifle doesn't make shooting fish in a barrel as much easier as it does in sniping' (or something like that).  

Hehe, Larry said that. It made him immortal. :)

"There are points wherein new circumstances will fail to have any impact on a given situation.  When shooting fish in a barrel, to use an extreme example, the addition of a sniper scope just doesn't make things easier."

The bell curve (even though, with two dice, the 'curve' looks like the silhouette of a pyramid) creates the 'diminishing returns' effect.  When your skill is 11 (in Scattershot, which uses a 'Your Skill Rating – 2d10 = success level' system) then a single +1 is a difference of 9%; when your skill is 14 a single +1 is 6%.  Following the scoped barrel-fishing model, a flat curve 'does bad things to modifiers;' so I guess I disagree with you here.

It's just that (and this goes along with the other thread about modifiers) it seems to me like a modifier should be as close as possible to having the same effect on every circumstance. That is, it seems like modifiers should be *independent* of skill... that sniper scope should always have the same effect on the skill... when compared to the existing skill that effect might be trivial, or it might not.

Let me put it this way: If you're chance of hitting a distant target in cover is 10% (1 on a d10) a +1 modifier is a big deal... it doubles your chance of success. But if your chance of hitting a fish in a barrel is already 80% or 90%, that +1 modifier makes much less relative difference. It still has close to the same effect (around +10%), it's just a lot more noticible in one case than in the other.

I dunno, though, maybe it's just two different ways of looking at it.

Let's do something easy like this. Everyone's used to rating things on a scale of 1 to 10, right? Why not say that your result is also rated on a scale of 1 to 10, indicated by a d10 roll, adjusted your skill. Let's say skills range from 1 to 5, average being 3. So your roll will be in the 4 - 13 range if you have a skill rating of 3.

That doesn't make any sense.  This says that you can roll well enough to beat difficulties that don't exist.  Skills are 1 to 5?  Problems are difficult from 1 to 10?  If you roll over 6 with a skill of 4 it beats non-existent difficulty levels.

Er, sorry, maybe I didn't explain that well. The system is (My Skill + d10 vs. Your Skill). Think of it this way: every action is given a rating on a scale of 1 - 10 by a single unmodified d10 roll. This scale slides up and down in relation to the scales used by other characters. This sliding is accomplished by adding the character's skill to the roll. So, for example, if my skill is 4 and your skill is 7, a result of '1' for you is actually 3 points better than a roll of '1' for me. How the three points of difference are interepereted would depend on the system. They could just be used to indicate success / failure, or they could be used for quality, and so on.

You're absolutely right, though, skills should be rated from 1 - 10 as well. Dunno what I was thinking of. :)

The difference between these Scattershot and Paganini's system is that, in his, the opponent is disempowered (when played by a player) or the sensation of 'threat' is reduced (there's more suspense waiting for the other die roll) because his is strictly an 'unopposed roll' system.  Scattershot looks like it is a fusion system when actually the 'faux opposition' is only supplying a variable modifier.

Hmm. So Scattershot is a sort of best of both worlds - it looks like one, but it functions like the other?

I know this is a really tough concept to grasp, I wouldn't have figured it out if I hadn't been working on a math minor in college.  (Well, it could be easy for you, but it wasn't for me.)  If you want, I can explain the mathematics of it in more detail in Private Message, if you're still not 'getting it.'  That goes for anyone who finds these maths, 'over their heads.'

Yes please. Although it's not so much the math that I'm having trouble with as it is the application. How are both sorts of rolls applied in practice? Could you put it in the context of some actual play? Just saying "Skill - 2d10 is your result" without any actual play context makes it a bit hard to get ahold of. :)

[Ring Kichard]

Mike,

Am I right in thinking this - and your other two rants - are mostly discussions about the scope of mechanics? You seem to warn us against causing unintended results in stat + skill systems, you warn us not to design more than we should in your article on combat, and you warn us not to follow wasteful design trends in your current article on opposed rolls.

If this is the case, I agree with your motives whole heartedly, elegance in game design requires restraint, or at least deliberate decision. I believe James Ernest wrote an excellent article on games with an eye to promoting a measured style of mechanic design. That is not to say that Cheapass games are sedate or conservative, only that they are designed with focused intent.

However, I do not see that this design (rolling opposed rolls sometimes and not others) is terribly inconsistent with good practice. In addition to possibly being an aesthetic decision, there are some kinds of consistency that would result in this sort of system. One consistent scheme would focus on the player and character instead of overall resolution.

To explain with an example, suppose a game had the rule, "whenever a character faces adversity, that character's player should roll 1d10." Consistent expansion of this rule would require that if two characters were at odds both of those characters' players would roll a die for themselves. This is a consistent mechanic, and while it does require interpretive guidance, it seems to be the founding consistency of many systems that use opposed rolls.

I think this is the platform from which I defend design mechanics that appear to be mixed. They are often the result of some other design consideration of equal value to consistency of mechanical interpretation. You mentioned earlier that there was a system in which only the players (separate from the GM) rolled dice. This apparent consistency is the result of an underlying inconsistency: the GM never rolls. Similarly, a consistent underlying mechanic, "everyone rolls," can create other mechanical situations that appear inconsistent. In fact I am hard pressed to think of a successful system that is universally consistent in every way.

Now, it is entirely possible that opposed rolls are included in many games for no better reason than tradition. Shaking people out of that rut is useful and good, and I wish I had the eloquence to do so myself. But I think in this case you have highlighted the negatives of a mechanic somewhat one-sidedly; but that's probably what makes this a rant.

[Mike Holmes]

Ring,

I think you have my motives mostly right. That is, people can make better games when they make informed decisions. I only point out the negatives to say that they exist, and so people know that they may be making a system that is not as good as it might be. If Wart decides that the aesthetics of the opposed roll/unopposed roll are important, or you decide that they are semiotically important, despite whatever downsides might exist, then you have at least made a considered judgment. Further, you can take steps to minimize the "negatives" of such mechanics (such as the problem with static actions having less fecundity than active ones), knowing that they exist.

Yes, if there is a deeper design consideration driving a split, then by all means one should go with the split in question. As I said, the Falkenstien split is a good one, as is the InSpectres Attribute/Stress split. The split I am arguing against is merely the traditionally uninformed adoption of the opposed/unopposed mechanic. Usually, what happens is that a particular mechanic is made that addresses either the opposed situation, or the unopposed situation, and then the designer goes, "hmmm, but what if the other situation occurs?" and promptly designs a second method for that case. The process should be to recognize that both "cases" (fictional, really) can occur, and make a single system that addresses them both from the start.

If designing a game from the ground up, one can still have the consistencies that you discuss using a single system. I think that people are looking at this discussion and saying, hmm, how would that work if I tried to make GURPS into a single roll type system? Well, it probably won't. GURPS wasn't designed with this point of elegance in mind, and small adjustments won't be able to bring it in line. You'd have to rewrite most of the resolution (at which point you might as well just write your own game anyhow). These rants are advice to designers making new games, and from that perspective, you can make such systems work just fine (often with less effort than trying to come up with the dichotomous method; at the very least it's that much less writing).

What you call "consistent" is only so from one POV. It is the standard POV of the industry, but not one that necessarily be taken. In InSpectres, for example, there are no simultaneous contested actions. If I attack you, I just roll, and see how well I did. Your assumption springs from the idea that the opponent's ability must be allowed to counteract the acting characters. This does not need to be so to have an effective system. Not that I'm saying that all systems should discount this, but just to show that there are other POVs as well. Even in a system that does have the standard assumptions about opponent's resisting, however, you can just take turns. I attack you; I roll against your DEX as a target. You attack me; you roll against mine. In fact this is exactly how resolution was done in systems like D&D before skills came along, as I describe in the history of the problem.

If you must have simultaneous opposed actions in some cases, then I suggest that all rolls be opposed. Again, this is why I like this method, and you seem to simply be arguing for my favorite system. Put it this way, what is inconsistent about always rolling an opposition to every character roll? Some people find it odd somehow that I would roll to see how well a lock resisted being opened. But it's just a statistical system for determining degrees of success/failure, I'mnot really rolling for the clock as though it were a character. Most people get over such aversions quickly after just trying it. I think the bias only exists at all because of the tradition. Or, rather, it doesn't aesthetically bug newcomers to RPGs in any way. In fact, it makes a lot of aesthetic sense to me, personally; it makes every conflict fell like a contest as opposed to just tasks.

To sub-rant for a moment, there are all sorts of other advantages to all opposed rolls. As Fang points out, you can get what Mega-Traveller used to call the "Uncertain" roll. Where the player only knows half of the result. This can be used to all sorts of cool effect. Also, you can roll fewer dice and still get more complex curves. Just rolling one die for each side, for example, you get the nice pyramid curve (which has a good mix of reliability and flexibility). Also, it allows for very good ranges, ranges unachievable with target systems.

Anyhow, to sum up, by looking at these sorts of things up front, one can certainly get a better result than if one merely trusts to tradition and includes mechanics just because other games have.

Mike

[Le Joueur]

I can explain the mathematics of it in more detail in Private Messaging, if you're still not 'getting it.'  That goes for anyone who finds these maths 'over their heads.'

Yes please.

Okay, going to PM.  Anybody want further info, PM me please.

Fang Langford

[damion]

I've been lurking here(this thread) a while and came up
some questions, just to play Devil's advocate a bit.
Note:I apologize in advance for stupid questions/points.

One thing it seems to me is that this is only a problem    
if you have a situation where both an un-opposed roll and an
opposed role make sense. For instance, an unopposed combat roll makes no sense. If all thing are either opposed or unopposed, admitably, you have decide which is which, but historically that isn't much of a problem( is there an opponent who  can get a variable result?).
Thus you have a consistent system, in that unopposed rolls
have one distribution, and opposed have another.

Also, I can see aesthetic value in having a contested roll have a different distribution, as someone is activly trying to foil one, this models the 'feedback' of such a situation.

Also of course, there are two types of opposed events.
1)Non-Zero sum.
Frex:Consider an art contest-I make my piece, you make yours, the objectivly better one wins. You got X, I got Y. Say I win, the 'goodness' of your piece does not reduce the 'goodness' of mine. I.e. mine is just as good as if I'd just made it normally. This method I think is valid. Correct?

2) Zero-Sum
I think this is the thing your objecting to. I.E a better 'loser' roll reduces the degree of success of the winner.
This I believe is the 'invalid' method.  Correct? Or in other words this is what you advocate for all-opposed systems.

all-opposed systems have the following problem in my Mind
Variablity of static quantities/Non-reproducability
This isn't a problem when comparing a static to a dynamic quantity. The Dynamic quantity absorbes any wierdness.
However when you compare static to static, strange things can happen.  
I can use my board with Very Long[3] to get across the Wide[3] chasm, but that doesn't necessaraly mean I can use the board on the way back. Another way of look at it is if
I Jump with 2 success on the way across, I could have the same number of succeses on the way back and not make it.
Also, if we want to figure out how far I jumped, how do we do that?
An application of common sense can fix things like this, but it is troubling.

Various other comments:
I think it should be noted that GM's can like to roll dice also.

:)

[Jake Norwood]

Just thought that I'd point this one out, since this is part of a serious of (very instructive) rants on gaming assumptions...

Here's an assumption:
Multiple resolution types (e.g. opposed/unnopposed, etc.) are a bad thing.

Is this the case? Many of us assume so...

Jake

[Paganini]

Just thought that I'd point this one out, since this is part of a serious of (very instructive) rants on gaming assumptions...

Here's an assumption:
Multiple resolution types (e.g. opposed/unnopposed, etc.) are a bad thing.

Is this the case? Many of us assume so...

New thread, Jake, my friend. Time for a new thread. :)

[Mike Holmes]

Just thought that I'd point this one out, since this is part of a serious of (very instructive) rants on gaming assumptions...

Here's an assumption:
Multiple resolution types (e.g. opposed/unnopposed, etc.) are a bad thing.

Is this the case? Many of us assume so...

I agree with Nathan that this could be a whole new thread. OTOH, I will say this: If a particular resolution system provides little or nothing that can't be gotten from having it just be a particular application of some overall system, then it's definitely a bad thing. It's complexity without a return, and other potential hazards. That's the only point I'm arguing here. If you have a good, well thought out reason for multiple systems, then fine. It's just that I can point to many, many that have fallen into this particular trap where an assumption of necessity exists where there is none.

Mike

[Jake Norwood]

Just poking my head and and seeing if that question was a valid concern in this thread. For the most part, I agree with everything I see here, but I wanted to see if we hadn't built up 2 pages on another assumption.

A pleasure reading these, as always, Mike.

Jake

[Mike Holmes]

Hi Damion,

Don't apollogise, you've got some really good concerns. Not that I don't have answers, though... :-)

One thing it seems to me is that this is only a problem    
if you have a situation where both an un-opposed roll and an opposed role make sense. For instance, an unopposed combat roll makes no sense.

My point was that there are no "unopposed" situations, ever. You are always going up against the difficulty of the roll whatever that represents. That's the myth, that there are two kinds of situations requiring two methods to resolve. There is only one: opposed. There are many ways to simulate this, however, using methods that were formerly only used for "opposed" situatiuons, vs. those used for "unopposed" situations.

If all thing are either opposed or unopposed, admitably, you have decide which is which, but historically that isn't much of a problem( is there an opponent who  can get a variable result?).
Thus you have a consistent system, in that unopposed rolls have one distribution, and opposed have another.

Again, that's the in-game description. You are assuming that a die roll in appropriate situations simulates this better somehow. It does not. Mathematically they are equal. See the original post.

Also, I can see aesthetic value in having a contested roll have a different distribution, as someone is activly trying to foil one, this models the 'feedback' of such a situation.

Sure, I admit to that argument. However, most differentiated systems actually provide completely contradictory feedback. That defeating an active opponent is something that it less random than defeating a passive one. This can be fixed by difficult methods, or the situation can just be ignored, which solves the problem more simply and easily.

Also of course, there are two types of opposed events.
1)Non-Zero sum.
Frex:Consider an art contest-I make my piece, you make yours, the objectivly better one wins. You got X, I got Y. Say I win, the 'goodness' of your piece does not reduce the 'goodness' of mine. I.e. mine is just as good as if I'd just made it normally. This method I think is valid. Correct?

2) Zero-Sum
I think this is the thing your objecting to. I.E a better 'loser' roll reduces the degree of success of the winner.
This I believe is the 'invalid' method.  Correct? Or in other words this is what you advocate for all-opposed systems.

all-opposed systems have the following problem in my Mind
Variablity of static quantities/Non-reproducability
This isn't a problem when comparing a static to a dynamic quantity. The Dynamic quantity absorbes any wierdness.
However when you compare static to static, strange things can happen.  
I can use my board with Very Long[3] to get across the Wide[3] chasm, but that doesn't necessaraly mean I can use the board on the way back. Another way of look at it is if I Jump with 2 success on the way across, I could have the same number of succeses on the way back and not make it.
Also, if we want to figure out how far I jumped, how do we do that?
An application of common sense can fix things like this, but it is troubling.

Very astute. There are simple solutions to these things, however. First, in the case of the board and bridge, there is no contest between two static things. As always, as in every RPG, simply use karma for comparison. In the case above, depending onthe system, the board will always reach, or it never will. I would never suggest rolling in such a case. I do not pretend that there are no differences between active and passive things, I only claim that there are no unopposed contests. That is, after all the definition of contest. You can find implicit definitions of this in most RPGs. They go as far as to say that even if it looks active, like walking across the street, even then it is not a contest. So, the blurry line is obviously drawn fairly far to the side of only rolling for contests where there are very active things occurring. OTOH, if you want to roll, for some reason, the "all opposed" system is there to support you. For example, if you defined the chasm as Widening (3) indicting that an earthquake was making finding a reasonable edge on which to place the board difficult,then the system might reasonably be used. As always this has to be a GM call.

You cannot "fail" with "2 successes", that would require one or more failures. That is, the result of your own roll says nothing in an "all opposed" system about how well you did. Only the end result does. Successes, are determined by how much you exceeded your opponent's roll. Note that in Synthesis, we go out of our way to call dice that come up positive Evens, and not Successes. They aren't Successes until the opponent's Evens are subtracted. Same thing in Sorcerer; there is no personal target, your successes being the dice that are higher than your opponents.

With the zero-sum vs. non zero-sum thing, the non-zero sum art contest would probably be separate contests against an arbitrary difficulty to create an object of beauty. The more talented the artists, the more difficult the medium, likely, but any diffculty will do, including zero for some systems. And then once created, the objects are compared. In this case, you are rolling more dice, and the results are more certain.

This is like the opposed/unopposed problem in that you are rolling more dice in this case to get the end result. Except in this case it is justified as we are looking at successive comparisons in what are likely to be certain sorts of situations that are likely to be tight. Or IOW, it is precisely the non zero-sum sort of competition that is likely to produce reliable results. Thus, in our example, the static art contest would be more predictable than the active fight. Which was what we expect.

The more comparisons, the more likley that the expected result occurs. And it still all only uses the one system. Note how in such a system these comparisons can continue ad infinitum (or they can compete in some systems). We can compare your win in the contest with how well Bob won last year. All using only the one mechanic, which is cool. BTW, for those who want to "fix" an opposed/unopposed system, mechanically, this is what I suggest (normalizing dice, or having more rolled in the case of static attempts instead of active ones).

That was stated a bit muddily, did it make sense?

I think it should be noted that GM's can like to roll dice also.

Sure GM can like to roll dice. I do sometimes. Thus I would never exclusively GM InSpectres, personally. OTOH, nothing I've said precludes GMs rolling and players rolling. I've just brought up InSpectres as a system that can work with only one side rolling. Again, these are just the options on the actual system, and have nothing to do with the main claim that one resolution system for both cases of opposed/unopposed rolls.

Mike

[Walt Freitag]

Hey Mike,

I agree with most of the principles about game design you've been discussing.

However, for the past few days I've been contemplating the supposed counterintuitive lesser "reliability" or greater "randomness" in the classic "unopposed" roll (die roll plus skill vs. a fixed target number) as compared to the classic "opposed" one (die roll plus skill vs. die roll plus opposing skill). And I'm just not seeing it.

"Reliablity" and "randomness" are not mathematically precicse terms, of course, so let me try to define them. If system B is "more reliable" or "less random" than system A, then we should be able to say one or more of the following about them:

1. The probability of success in system B is farther from 0.5, making it easier to correctly predict whether the outcome will be success or failure in system B.

2. Certain specific levels of success (or failure) are more likely to occur in system B than in system A, making it easier to correctly predict the exact outcome in system B.

3. An outcome that falls within a central range, such as -3 to +3 (or in any specific range) is more likely in system B.

4. The overall expected level of success or failure is of lesser absolute value magnitude in system B.

5. In the subset of outcomes in which success occurs, the mean level of success is of lesser magnitude in system B.

6. Ditto 5, for failure.

7. The effect of a given numerical advantage or disadvantage (say, a difference in the character's skill level) on the chance of success or failure is greater in system B, making success or failure easier to predict (more reliable) in system B when one side has an advantage.

8. The effect of a given numerical advantage or disadvantage on the expected degree of success or failure is higher in system B.

Clearly, number 1 is not applicable. Either type of system can easily be set up to produce the desired probabilities of success, so "reliability" can't be based on that alone. It must instead have something to do with the overall distribution of degrees of success and failure, or on how predictably the outcomes are affected by advantages or disadvantages.

To examine the other possibilities, let me set up a simple "system A and system B" as they might appear in a game system that uses both opposed and unopposed-style rolls. System A, with the hypothetically lesser reliability, will be the typical unopposed roll. It's a d10 plus skill vs. to roll higher than a fixed difficulty level assigned by the GM or specified in a table somewhere. The difference between the die roll + skill and the difficulty is the degree of success. System B for "opposed" rolls is d10 + skill vs d10 + opposing skill, with the difference again being the degree of success. In both cases a tie is allowed (success/failure level of 0).

Starting with evenly matched examples, we have in the A case d10 + x against a difficulty of 5 + x, with the outcome distribution:

Code Select Expand


SYSTEM A
outcome       +5  +4  +3  +2  +1   0  -1  -2  -3  -4
probability   .1  .1  .1  .1  .1  .1  .1  .1  .1  .1


In the B case we have d10 + x vs. d10 + x, with the outcome distribution:

Code Select Expand


SYSTEM B
outcome        +9  +8  +7  +6  +5  +4  +3  +2  +1   0  -1  -2  -3  -4  -5  -6  -7  -8  -9
probability   .01 .02 .03 .04 .05 .06 .07 .08 .09 .10 .09 .08 .07 .06 .05 .04 .03 .02 .01


Okay, now, do any of our suppositions for "B is more reliable" hold up?

1. Already shown to be N/A

2. No. Zero successes (a tie) are equally likely; all other possibilities are LESS likely in system B.

3. No. The opposite is true in all cases.

4. No. The opposite is true. In A it's 2.5, in B it's 3.3.

5. No. In A it's 3.0, in B it's 3.67.

6. No. In A it's -2.5, in B it's -3.67

7. No. In most cases the change makes more of a difference in A. In other words, an advantage or disadvantage is usually more likely to swing the outcome in A. Subtract 4 from the character's ability score, for example, and his chance to succeed is now 0.1 in A, 0.15 in B.

8. No. In both cases an advantage of +1 greater ability adds (this one's easy) 1 to the expected outcome. Same deal for disadvantages.

So, that's my dilemma. I cannot see any basis for calling B "more reliable" or "more predictable" or "less random." But I can see good reasons for calling A so, which would conform to everyone's intuitive expectations.

What seems to happen is that in B, the wider range of outcomes more than makes up for the "pyramidal" concentration of outcomes in the center. B would be more reliable ony if you were to normalize the two outcome distributions to the same absolute range before doing the comparison. But no system I'm aware of does that, nor does it seem a justifiable thing to do under the circumstances.

- Walt

[Mike Holmes]

In the case I was displaying it is exactly number one that is the problem (assuming I understand you correctly. We can debate these criteria in another thread, if you like). Yes, it can be avoided, it just usually is not, and is not in the example. There are lots of ways that you can reverse the nature of the curves should it suit you to do so. Roll Skill + 2 dice - 2 dice vs. target for "unopposed" situations, and Skill +1 die vs. Skill +1 die for "opposed". This makes the unopposed more reliable by my definition. Or go with Skill +1 die - 1 die vs. target to make it completely even distributions between both opposed and unopposed if you don't see either situation as being more or less reliable. The problem is again, the addition of a system without a need for one (you'll note in the balanced option that the only real difference is who rolls the dice; why not have each player roll one in every case, the GM for "passive" things as well as NPCs?).

So it's not that opposed rolls always have these sorts of math problems automatically, it's that they often do because people do not realize that such a system has such potential probelms. This is just one problem that can occur with such a system, BTW, the one I happened to throw out there. It's just what tends to occur when you do not apply rigorous analysis to your system, and just trust to tradition to provide you with proper tools. Which is all I'm warning about. My simple solution? Just avoid it altogether by not having the dichotomy. Note that in my favorite version, that I do allow such an idea in, but intentionally and to serve my own design purposes.

Mike

[contracycle]

Question and request for assistance from Mike:

1) I was rereading Blue Planets mechanics last night and noticed this issue and one other (see below).  I'm considering a rewrite of BP's mechanics to make them a bit lighter; to this end I'm seriously considering breaking their opposed roll system into something like whispering vault, where all rolls are made byt eh players.  I feel (without serious evidence, admittedly) that this might reinforce the "you are dependant on your own actions" feel I would like to promote to support a theme of wilderness survival.  My questions therefore are a) are you familiar with the system, b) what do you think of the general principle, c) do you think an anomalies would arise?

2) Just as an appendix of your standard rant: given that I was looking at the system in consistency terms, how do you feel about the completely seperated initiative mechanic?  This is a common if elderly feature of RPG systems: a different, and usually mor erandom, mechanic for generating action order.  Any thoughts on that?

[Mike Holmes]

Question and request for assistance from Mike:

1) I was rereading Blue Planets mechanics last night and noticed this issue and one other (see below).  I'm considering a rewrite of BP's mechanics to make them a bit lighter; to this end I'm seriously considering breaking their opposed roll system into something like whispering vault, where all rolls are made byt eh players.  I feel (without serious evidence, admittedly) that this might reinforce the "you are dependant on your own actions" feel I would like to promote to support a theme of wilderness survival.  My questions therefore are a) are you familiar with the system, b) what do you think of the general principle, c) do you think an anomalies would arise?

I am not familiar enough with BPs mechanics to comment (ironically, I was just thinking about buying it yesterday). However, it sounds like it is exactly the sort of candidate for "fixing". What you must look at is whether or not the currency that comes off of the roll is used further. In most opposed systems for skill contests, it is not. That is to say that the difference in rolls simply determines who wins (binary pass/fail). Some systems consider the magnitude of the difference to mean something, however, and that is where you can run into problems converting. Proceed with care, however, and I'm sure that you can alter it to suit.

If you care to give me more system details, I could comment further. Or, better yet, if someone else knows the system, they might be able to comment.

In any case, Whispering Vault is a very good example of a unified system, and working off something like that would produce your desired effect.

2) Just as an appendix of your standard rant: given that I was looking at the system in consistency terms, how do you feel about the completely seperated initiative mechanic?  This is a common if elderly feature of RPG systems: a different, and usually mor erandom, mechanic for generating action order.  Any thoughts on that?

Separate initiative mechanics? First, see Mike's Standard Rant #3: combat systems. I think that for a game that proposes to focus on the politics of ecology, dropping any variance in the combat system from the standard resolution system would be a good idea. Again, not that there should never be violence in such a game, just that the rules should not privilege combat in any way. Make the game truely about the politics of ecology and nothing else, primarily.

That said, if you do have a separate combat system (using the Whispering Vault method), simply assign a target difficulty based on the target's skill, and roll. Success means that the player gained an advantage, or wounded the opponent. Failure means the opponent similarly gained the upper hand. For a great treatment of positional incrementalism (or the answer to, "why wouldn't I choose to wound?") see Paul Elliot's Zenobia. Voila, no initiative.

Initiative is really a holdover from wargaming more than anything else, and as uch is executed with the sort of ambiguity that is necessary for mass combat. Not that initiative isn't an element of single combat IRL. Just that in single combat it is a matter of skill and ability, and part of the randomness of fighting, and very much has nothing to do with who strikes first per se. Take for example the fact that attacking first is often a mistake in RL. TROS simulates this very well, which leads to realistic circling and other defensive behaviors. On this scale, we can simulate this easily by simply making it part of the success/failure mechanics.

I can't recommend this modification enough. My grognardiest players comment on how much more realistic combat is once you get away from the I swing/you swing combat. In more general terms, the only good reason to have a separate mechanic for anything is to shine a particular light on that facet of the game, to give it more focus. So, in TROS, of course there is a separate initiative mechanic; the game is all about combat. I don't get that vibe from Blue Planet.

Mike