A few years ago I analysed the hit and glitch probabilities used in Shadowrun Fourth Edition. The end result was the following amended glitch rule:


If more than half of the dice pool rolled come up as 1s, or if exactly half of the dice pool rolled come up as 1s and all the other dice come up as 2s, then a glitch results.


I have now finally got around to creating a web page that contains the information.

Wow. Sometimes I forget how much of a geek I really am. I see the title, "An analysis of the dice mechanic" and I go "ooooooh". I read the actual analysis, and I go "aaaaaah!"

Thank you for the analysis, Mr. Wizard.

Here is another thing to think about. Assuming 3 is the average attribute, and skill level 3 is equal to a professional, then most trained professionals have 6 dice to play with. This means they will have a glitch of some kind 3.5% of the time. If you hand craft 100 items in a day, two will have some minor defect, but remain functional, and one would be a total failure. AND, considering they will probably have some Edge on the average day when they have the average glitch, they can negate it. Maybe one or two total failures during a work week. This is why the world runs fairly smoothly, and why we don't bother to roll for every single little thing in the game.

(Yeah, okay, so I should bottle some of this geekness.)

On the other hand, on a bad day, during a dangerous run when your luck has run out, and you face competent enemies at night, in the rain, with some injuries, all your implants, talents and skills might not keep you from slipping on the grease spot as a round jams and goes off in your pistol.

Just a quick note:

Whenever your amendment kicks in, the result is a critical glitch. Is that right? So the ratio crit. vs. non-crit. varies between even and odd dice-pools. Also the overall chance of glitching tends to be lower.

Well, we noted the same effect you did and your first approach was to say more than half of the dice have to show one's. However, that just shifts the disadvantage from even pools to odd pools and makes glitches in high-power regions of the game even less likely.

In the end we gave up on the problem as in the real game most dice pools are much larger than 6 and the effect is hardly noticable. Just one guy, who has a Charisma+Etiquette pool of exactly 2 (Charisma 3, no Etiquette, so basically the standard guy) and was made fun of once to often, now insists on his right to default to no success or at least be allowed to just throw one die to minimize glitch probability.

It's good and useful to do more dice mechanic analysis. Much appreciated, by the way.

ugh, im really rusty when it comes to probability maths...

It may seem like that for a dice pool of 2 as with the amended rule the chance of a glitch is 0% but at the same time the chance of a critical glitch has been reduced from 19% down to 8%. I don't like the way the probabilities work in dice pools of 1 and 2 and so have a house rule called Zilching that specifies a minimum dice pool of 3 together with a negative dice pool. You can check it out in the house rules section of Wizard's Node.


The amended rule reduces the chance of a glitch or a critical glitch in even dice pools. It has no effect on odd dice pools.

Take a dice pool of 2. The dice roll as 1 and 3. Without the amendment that would result in a critical glitch, with the amendment it is simply a miss.

If the dice roll as 1 and 5 the amendment changes the result from a hit and glitch to just a hit with no glitch.

You are right. I didn't think of that. (Rare post on a forum)

Zilching sounds interesting. Did you make an analysis as to how this changes odds for 0,1,2,3 hits achieved?

However the 6 again rule seems a bit much for me. I already hated the 10 again in nWoD as it produces an extra-long dice-rolling procedure. I am already frustrated enough as it is that my players sometimes seem sooo slow to count out their dice and their results. Especially our Troll player, who loadly counts 1,2,3,... 22 for every single soaking roll and then again 1,2,3... for the hits. And sometimes he forgets how many Soak he has while counting and then re-calculculates and then he starts counting all over again... Makes me want to hit him and not hit him at the same time, if you know what I mean. At some point another player gifted him 22 dice, but he didn't even get the joke. To his defense: it is his kind of character acting, when he plays his full-cybered hacker,again with gazillion armor, he always has the pool stacked up in a neat little pile.

I always found it helpful to have my commonly used pools written on a sheet of paper and my dice arranged in groups of some size. Maybe 5 works best. I mean, 5 = 2 + 3, and 2 x 5 = 10. Chunking up the dice helps you build larger pools quickly, and having a cheat sheet for your pools allows you to build them up and then use tactile mathematics for the variable modifiers.

Might take a while for your player to get used to it, but it'll probably help him get his pools together faster.

No I haven't analysed it in detail. If my maths is right I do believe that the statistical average is the same for either the result of just rolling 1 dice or rolling 3 dice minus 2 dice. The difference being when you roll the 3 dice you have a broader result set with the remote chance of up to 3 hits.

@Heath: I tried all kinds of tricks to get him to count faster, but he considers it his personal spleen.

@Wizard: I agree with your math.