Game Design: Good average chances of success for all situations?

[Kariotis]

When designing new systems or homebrewing existing ones, one of the areas where I still often question both my experience and my gut feelings are the target values for average chances of success on a given roll. One thing I've been doing for a long time now is use a simple matrix that always remained the same, whether I was designing dice pool systems, roll-under-mechanics, used D100s, D20s or even playing cards. I only controlled for skill level and circumstances of the roll and left everything else out in order to not make it too complicated.

I didn't use the exact values I came up with, I used them as rules of thumb (depending on the dice used, it wouldn't even have been possible to hit the precise values). In some cases I deviated a lot from individual values, but rarely much from the general distribution as a whole.

It has always seemed pretty important to me to consider the average success rates at different skill levels from the absolute lowest to the absolute peak. If the success rate is too high, the game may become too easy, and players may become bored or disengaged even if they're happy their character is decked out. If the success rate is too low, the game may become frustrating and discouraging instead of challenging.

So whenever I designed a new game, or started homebrewing an existing one, this has been one of the first things I did and then I always keep my eye on it during the design process. Trying to make sure that the development over the skill levels is smooth with a couple of bumps here and there to signal skill thresholds, and that even difficult tasks are sometimes accomplished while peak performers rarely fail provides players with a satisfying level of challenge and a sense of accomplishment. My hope is always that by balancing the difficulty of tasks and the modifiers that affect success rates, the system becomes more engaging and immersive.

So if you've been using something similar, this thread is for any GM and designer who wants to share their target values (or wants to take it as an opportunity to write them out in detail). This is essentially a poll thread - I don't mind a bit of discussion, but our focus here should be on getting as many replies with concrete numbers as possible to get an overview. I removed my own values for now in order to not poison the well.

 

[pemerton]

I don't have examples, but will cheerfully bump your thread!

But also have a question: mightn't it depend on other features of the system? Eg Burning Wheel deliberately has quite low chances of success (and hence quite high failure rates) compared to 4e or 5e D&D, because of the different way that failures unfold and the different significance low chances of success have for PC development.

 

[Fenris-77]

My first instinct here would be to start pulling the system and character design apart to look for tiers and core bits. Set next to that would be whatever the genre expectations are for the game in question. So a zero-to-hero OSR game has very different expectations for starting character competence than does a game like, say, Delta Green. Once you have those general expectations in hand you can start talking about how many skills at what level best represent that. A related addendum is a hard look at character advancement - the faster characters gain significant 'power' the lower they can start on the power scale, almost regardless of the above concerns.

 

[GMMichael]

When designing new systems or homebrewing existing ones, one of the areas where I still often question both my experience and my gut feelings are the target values for average chances of success on a given roll. . .

Why not take another step back and ask, "what is success?" " What if the game uses fuzzy outcomes instead? "

It has always seemed pretty important to me to consider the average success rates at different skill levels from the absolute lowest to the absolute peak. If the success rate is too high, the game may become too easy, and players may become bored or disengaged even if they're happy their character is decked out. If the success rate is too low, the game may become frustrating and discouraging instead of challenging.

This sounds like a problem for GM-less games, but I don't see how rolls can be too easy or too hard with a GM (or in my case, a GM armed with dice) who determines what the roll results should be/exceed.

Is this another way of saying "I don't want my monster manual to have statistics that are too low?"

 

[Leatherhead]

Given the principles of loss aversion (where a loss is twice as bad, as a win is good): A character that is supposed to be competent at a task should produce a desirable result ~67% of the time. Desirable results include;' success, exceptional/critical success, and falling forward with minor or negligible setbacks. Undesirable results include; null results (whiffing), falling forward with significant setbacks, failure with resource drain, and exceptional/critical failures.

 

[Krachek]

Repeating task like hitting in melee should aim 2:3 or 3:4.
note that these odds are cultural. 40 yers ago hitting 1:2 or even less was much more expected.

 

[kenada]

My homebrew system uses degrees of success and (mostly) fixed target numbers, so I calibrated the results around the spread I wanted and how that interacts with progression. I use AnyDice and write software to look at the results (depending on the complexity of what I want to examine). The latter is mostly necessary when exploring abilities that do something a little weird that doesn’t model nicely on AnyDice.

My system uses fixed difficulties (for the most part). It’s 2d10 against the following spread:

• Critical Success: 23+
• Complete Success: 17–22
• Mixed Success: 11–16
• Failure: 10−

Characters have attributes ranging from −3 to +3 and skills with ranks from +1 to +5. Making a Skill Check untrained imposes a −4 penalty. Working Together can add an additional modifier, and you can sacrifice things to increase the degree of success (e.g., bribing a guard, adding extra materials to a craft). Below are the percentage chances of success broken down over the range of modifiers (AnyDice link).

Modifier	Failure	Mixed Success	Complete Success	Critical Success
−5	85%	14%	0%	1%
−4	79%	20%	0%	1%
−3	72%	27%	0%	1%
−2	64%	33%	2%	1%
−1	55%	39%	5%	1%
+0	45%	45%	9%	1%
+1	36%	49%	14%	1%
+2	28%	51%	20%	1%
+3	21%	51%	27%	1%
+4	15%	49%	33%	3%
+5	10%	45%	39%	6%
+6	6%	39%	45%	10%
+7	3%	33%	49%	15%
+8	1%	27%	51%	21%
+9	1%	20%	51%	28%
+10	1%	14%	49%	36%
+11	1%	9%	45%	45%

Note: Percentages are not cumulative.

Characters have starting attributes of +0, so one with at least a +1 skill rank is looking at a ~64% chance of some kind of success. As you go up, the distribution shifts to better quality success. This spread was inspired by PbtA games. I feel like it gives a nice sense of progression while still working within the constraints of static difficulties, which I want as part of maintaining the neutrality of the referee. There are ways to shift the difficulty up and down, but it’s meant to be based on the framing of the scene and/or consensus. If a challenge is a HQ one, it seems like it should be harder. Still a WIP there though.

Combat is a little different in that the target Armor is not fixed (= 11 + armor proficiency + one of Dodge, Block, or Parry), but it’s intended to follow a similar spread (more or less). I could use a fixed target, and the Armor provides a modifier to your roll, but then it feels like I’d have just reinvented THAC0 as THAC17 or something wacky like that.

 

[soviet]

There is no correct answer. You must first ask questions like:

• Who (thematically) are the characters?
• What does an individual roll represent?
• What other ways exist to manipulate the outcome of a roll?
• What is the purpose of play?
• What is the desired rhythm of play?

 

[Darth Solo]

The correct answer is 50% base chance of success doing anything modified by character ability.

 

[Lanefan]

I'd say there is no good blanket answer that can apply to everything in a game. Each individual case is different, and has a different expected success rate.

I mean, look at baseball. From the hitter's perspective, consistently succeeding at getting on base 1/3 of the time is pretty damn good. But that also means a pitcher's expected success rate in not allowing the batter to get on base is, ideally, higher than 2/3.