Talk:Item passive stacking

Chance Stacking
I believe there is a mathematical error in the example on 'chance stacking'. When a hero has both Daedalus and Crystalys, you don't get 25% chance for Daedalus, 20% chance for Crystalys and 5% chance to proc both, for what I know.

Instead, you get the following:
 * chance to proc ONLY Daedalus: 25% for Daedalus * 80% for not proccing Crystalys = 20% chance
 * chance to proc ONLY Crystalys: 20% for Crystalys * 75% for not proccing Daedalus = 15% chance
 * chance to proc BOTH:          25% for Daedalus * 20% for Crystalys = 5% chance
 * total chance to get any proc: 20% + 15% + 5% = 40% chance

Now, I'm aware that a mathematical calculation like this will probably only make the article too confusing. So I think it might be better to just change the wording instead.

So instead of:
 * "If a hero buys a Crystalys, and then a Daedalus, on every hit the hero has a 25% chance of receiving the Daedalus critical, a 20% chance of receiving the Crystalys critical, and a 5% chance of receiving both"

...which wrongly implies you have a 50% chance to get any critical, I would put something like this:
 * "If a hero buys a Crystalys, and then a Daedalus, on every hit the hero has a 25% chance of receiving the Daedalus critical and a 20% chance of receiving the Crystalys critical, both of which include an overlapping 5% chance of receiving both, resulting in a total 40% chance to receive any critical."

or this:
 * "If a hero buys a Crystalys, and then a Daedalus, on every hit the hero has a 20% chance of triggering only the Daedalus critical, a 15% chance of triggering only the Crystalys critical, and a 5% chance of triggering both"

A similar error seems to have been made in the calculation with the MKB's:
 * MKB bash chance: 35%

>>lol, why 65%? correct answer should be 0.35*0.35*2 = 24.5%
 * Chance of triggering both bashes: 35% * 35% = 12.25%
 * Chance of triggering only one bash: (35% * 65%)*2 = 45.5%  (instead of 2*35% - 12.25% = 57.75%)

I should note that I haven't tested this data ingame. I'm just assuming it uses the mathematically correct way of combining chances.


 * You are correct. The language should indeed be corrected to reflect the actual probability. -Baloroth 20:52, 30 March 2012 (UTC)

Crit Priority
Apparently, if multiple crits are triggered simultaneously, the game gives priority to the crit with the highest multiplier, not the one that was acquired last: http://dev.dota2.com/showthread.php?t=5071. Someone should adjust the information accordingly. Would be really nice if Valve explained how all these low-level mechanics work themselves but oh well. --Pigbuster 04:45, 5 July 2012 (UTC)
 * . I also update the note on MKB, since that stacks on ranged and melee now just fine. -Baloroth 16:27, 5 July 2012 (UTC)

Evasion
"Only the highest value works per instance."

Evasion stack multiplicatively according to 6.79 changelog.

On other pages it is mentioned that evasion "stacks diminishingly" which is completely wrong. For example 1 Butterfly gives 35% chance to evade, thus 65% chance to be hit. This means a survivability of 1/.65 = 1.538... or 54% increase. Two Butterflies give a total of 57.75% chance to evade, or 42.25% chance to be hit. A naive interpretation would lead one to believe that this is "diminishing returns" since 57.75 < 35 * 2. But running the numbers will indicate the survivability is 1/.4225 = 2.366... or 136% increase in survivability.

But wait, what's 2.366.../1.538... ? Well it's 1.538... exactly the same as the value of a single Butterfly. Evasion does not have diminishing returns, it has multiplicative returns that increase by a linear factor. It's easy to see with an imaginary item with 50% evasion. The first would double your health, the second quadruple, the third would give an x8 multiplier, and the fourth an x16, etc. You can clearly see each additional item multiplies by 2.

Misunderstanding of evasion and armor as being "diminishing" is probably one of the most common mechanical misunderstandings around.