Do effects stack?

[Dragonredux]

Like for example, Crest of the Blackhammer clan gives me a 25% chance, that incoming attacks do 80% damage. So, let us say I have two Crest of the Blackhammer clan effects do they a 50% chance, that incoming do 60/80% damage.

The same scenario can be applied to the two different techs, like the Crest of the Blackhammer Clan tech kit and Bone lacing tech kit. Assuming the enemy's undead, both techs have a chance of doing the same effect except its 90% with Bone lacing.

[Alisto]

The effects are separate. You just have two chances to proc the effect - two Crests, each incoming attack has one 25% chance to proc the first 80% reduction, and then it has a 25% chance to proc the second 80% chance reduction.

Same for bone lacing I believe, an incoming attack has one 25% chance to proc crest, and then one...err, I forget the percent chance, but it has once chance to proc the damage reduction from bone lacing as well. Four Crests of the Blackhammer Clan would not provide a 100% chance for damage reduction.

[Tilithia]

The easiest way to see if they stack is to look at the blight resistance from Blackhammer kit. Since both of them add to your blight resist (+1000) id say effects stack too.

[hallucin8]

As a statistician, there's a lot of assumptions we have to make about the conditional probabilities e.g P(B=1|A=1)=0% or 25%... that is, can they actually both proc... but yer, it'd be pretty close to 50% chance if they each have a 25% chance.

[hallucin8]

So I got sidetracked at work and did some simulations in excel, and here are my results:
Probability that at least one item (each with 25% chance) will proc:
1 item: 25%
2 items: 44%
3 items: 58%
4 items: 68%

A quick check tells me this is correct, since the probability that at lease one item procs should be equal to "100% minus the probability that all items do not proc" (1 - 0.75^n, where n is the number of items).