variant skill checks

Drawmack

First Post
I want to make skill checks better resemble the bell curve to make calculating success rates easier. Though I'm going to do 2d10 - 1 unless a natural 20 is rolled. This does away with the 19 instead of the 20 because we count a natural 20 as a 30 and a natural 1 as a -10 so we maintain the critical success and failures but do away with almost criticals. What this does to the system is this.

Average Roll: 1.05 (or there abouts)

sets of rolls that can make any number
1 {1,1}
2 {1,2;2,1}
3 {1,3;3,1;2,2}
4 {1,4;4,1;2,3;3,2}
5 {1,5;5,1;2,4;4,2;3,3}
6 {1,6;6,1;2,5;5,2;3,4;4,3}
7 {1,7;7,1;2,6;6,2;3,5;5,3;4,4}
8 {1,8;8,1;2,7;7,2;6,3;3,6;4,5;5,4}
9 {1,9;9,1;2,8;8,2;3,7;7,3;4,6;6,4;5,5}
10 {1,10;10,1;2,9;9,2;3,8;8,3;4,7;7,4;5,6;6,5}
11 {2,10;10,2;3,9;9,3;4,8;8,4;5,7;7,5;6,6}
12 {3,10;10,3;4,9;9,4;5,8;8,5;6,7;7,6}
13 {4,10;10,4;5,9;9,5;6,8;8,6;7,7}
14 {5,10;10,5;6,9;9,6;7,8;8,7}
15 {6,10;10,6;7,9;9,7;8,8}
16 {7,10;10,7;8,9;9,8}
17 {8,10;10,8;9,9}
18 {9,10;10,9}
19 {}
20 {10,10}

% chance of any number
1 (1%), 2 (2%), 3 (3%), 4 (4%), 5 (5%), 6 (6%), 7 (7%), 8 (8%), 9 (9%), 10 (10%), 11 (9%), 12 (8%), 13 (7%), 14 (6%), 15 (5%), 16 (4%), 17 (3%), 18 (2%), 19 (0%), 20 (1%)

This means that most (44%) of the rolls will be between 8 and 12. So it heavily weights the die to the center of the scale. This way standard deviation plays a much larger roll in the game.

This will only be used for skill checks everything else will still be rolled with 1d20
 

log in or register to remove this ad

Seems fine to me, but keep in mind that the average for 2d10 is 11, and the average for a d20 is 10.5. That shouldn't make a difference, though. :)
 

Umm, I'm not sure what you're talking about but here is the math.

Doing away with 1:
(2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20)/20 = 10.45

doing away with 19:
(1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+20)/20 = 9.55

Also when you're talking about average rolls in this way that is not nearly as important to game mechanics as being able to anticipate the roll's result +/- 2 almost 50% of the time.

My question is, if you were a player would you feel jipped by this or would it be okay with you?
 

You're dividing wrong with the 2d10. There are only 19 possabilities, not 20. :) And it would be fine to roll like that. I, personally, like a bell curve better than a flat line.
 
Last edited:

In my humble opinion, I don't think it's something I would like as a player.

Using a 2d10 for skills (or some variant thereof) does have one major benefit: it better simulates real-world performance. After all, most times when you perform a skill you usually perform competently (you do an average job), and doing exceptionally good or poorly is somewhat rare. The bell curve distribution of a 2d10 models this much better than the linear probability distribution of a d20.

A 2d10 skill system puts a very heavy emphasis on ranks and bonuses instead of the die roll, which has a high probability of being close to 10 anyway. This sounds like a good thing, but let's analyze it a bit more.

Using 2d10 makes easy tasks easier, and hard tasks harder -- tasks with low DCs are now a cakewalk, but tasks with high DCs are now extremely difficult to achieve. Consider a difficult magical trap with a Disable DC of 33. For a 10th level rogue with a Dex of 14 and a maxed out skill, he succeeds on a die roll of 16+ in either the normal system or the 2d10 system.

Under the normal (d20) rules, he has a 25% chance of rolling the 16 or higher he needs (5% chance each for rolling a 16, 17, 18, 19, or 20). By the 2d10 system, he only has a 10% of rolling the 16 or higher he needs: 4% (of rolling 16) + 3% (of rolling 17)+ 2% (of rolling 18) + 0% (of rolling 19) + 1% (of rolling 20) = 10%.

In fact, the probabilities are very skewed for unopposed rolls. I'm using your percentage values above, which may not be exact, but are close enough:

[Die Roll needed to succeed] [d20 Success%] [2d10-1 Success%]
03+ : 90% vs. 97%
05+ : 80% vs. 90%
07+ : 70% vs. 79%
09+ : 60% vs. 64%
11+ : 50% vs. 45%
13+ : 40% vs. 28%
15+ : 30% vs. 15%
17+ : 20% vs. 5%
19+ : 10% vs 1%

For easy tasks the difference is actually in the player's favor. But when you start getting up to needing a 13+ to succeed, which isn't unreasonable at all for a challenging task, the player ends up getting screwed pretty badly. If you need a 17+ to succeed, you might as well forget about it.

The only way to fix this in 2d10 is to completely rebalance and recompute static DCs for unopposed tasks.

By this analysis, then, skill boosting items become extremely powerful, in that they affect your chances of success much more than in d20 (because in 2d10, easy tasks get REALLY easy and hard tasks get REALLY hard).

So in 2d10, an item that gives +4 to a skill has a more dramatic effect than an item that gives +4 to a save. Any item or class feature that gives +10 to a skill gives you a monumental boost. If you needed a 15+ to succeed before (15% chance), now you only need a 5+ (90% chance) -- that's a whopping 75% difference!

Everything in the core rules is designed to operate on a (+1 bonus = +5% chance of success) philosophy and the game is balanced with this in mind. A +1 means the same to everyone and is just as useful, no matter how hard the task is. In the 2d10 system, that isn't true (+1 bonus = anywhere from about +0% to +10% chance of success), depending on how easy the task is).

Opposed checks are less of a problem, but the probability skew makes it tougher to win an opposed check against someone who has a better bonus (ranks + ability score) than you because the results are less random (smaller variance). In the d20 system, you stand a better chance because of the larger variance. The more "random" nature of d20 is more suitable for a fantasy style RPG, I think, as it makes things less predictable (nothing is ever certain) and it makes heroic tasks with high DCs actually worth trying.


Don't get me wrong, I'm not criticizing you. it is your game, and you should do what you like. I even encourage other people to try new things. Some others in these boards have tried 2d10 and like it. I'm just trying to provide a detailed statistical analysis of why I think 2d10 is bad.

As a player, I don't think I would like the 2d10 system at all unless I were playing a game where 2d10 was the core mechanic for everything and the game system was specifically designed with it in mind. D&D is not this way.


Jason.
 
Last edited:

Most DCs are 15...

jlhorner1974 said:
But when you start getting up to needing a 13+ to succeed, which isn't unreasonable at all for a challenging task, the player ends up getting bleeped pretty badly. If you need a 17+ to succeed, you might as well forget about it.

Since most DCs are 15+, this sounds bad, especially at low levels, where +4 won't be enough to raise that 9.45 to 15+.
 

Remove ads

Top