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All of the latest Mists of Pandaria newsSome remarks on drop rates
by Eliah Hecht 
Apr 29th 2008 at 6:00PM
Let's say you read that Shattered Sun Supplies have a 10% chance to contain a Badge of Justice, and, excited, you go out and do enough dailies get 10 Shattered Sun Supplies. You open them all and find not a single Badge, or you find five badges. Do either of these outcomes mean the 10% drop rate is wrong? No! They do not! All a 10% drop rate means is that for each Supplies, there is a 10% chance that it contains a Badge. Random events have no memory, so no matter how many badges you get in the first nine Supplies, your chance to get a Badge in the tenth Supplies is still 10%. The traditional analogy is that if you flip a coin nine times and get heads each time, the chance of getting heads on the next flip is still 50%.
Now it is true that you will probably get a Badge in ten Supplies if the drop rate is 10%. If you're interested in how likely it is, here's the calculation to do. The chance of not getting a Badge in one Supplies is (100% - 10%) = 90%, or 0.9. Raise that to the tenth power, for your ten independent Supplies-opening events, and you get the chance of, ten times out of ten, not getting a Badge: 0.9^10 = 0.349, about 35%. So in fact, out of ten Supplies, you will get a badge (100% - 35%) = 65% of the time, about two thirds.
TL;DR version: A drop rate is a probability, not a guarantee.
Filed under: Analysis / Opinion
Reader Comments (Page 3 of 3)
cdb2000 Apr 30th 2008 8:37PM
I once got four crusader drops in two hours while farming for runecloth. True story. I win at statistics.
Mowgile Apr 30th 2008 6:47AM
@dacamper: Absoloutely. We had a wonderful superstition going on in my old guild (pre-BC) when went along these lines:
"Whenever X leads our raid, A,B,C items drop. Whenever Y leads our raid, D,E,F items drop. Therefor the algorithm Blizz uses to determine loot is somehow based on the name of the raidleader."
So we always put a different person in the raid leader slot, and varied the order we entered the instance in order to ensure a perfect loot distribution.
It never worked, of course, but people will believe anything once they see a pattern.
I've heard it said that there's a genetic imperative to see patterns and believe them. "Is that pattern of orange and black in the grass a tiger?" Could be urban myth, but it's a nice thought ^^.
Dan Apr 30th 2008 7:40AM
Yes, we are prone to recognize patterns. Take two humans, one recognizes patterns (A), the other doesn't (B). If they both find a large patch of different berry bushes, A would hesitantly try a berry, when he finds it's good he will eat only that type of berry (until they run out). When person B tries one, and find it's good, he will eat all the berries, and die from poisoning from that spiky berry which didn't at all fit the pattern that A found.
There's a name for the behavior of finding non-existant patterns when we know something has changed too, but I can't remember the name of it... But basically, if we know something has changed (a patch) we will automatically try to figure out patterns in what this effects, which results in that if you get less skillups while crafting right after a patch you will be certain that they nerfed crafting, even if they didn't even touch it.
con-man Apr 30th 2008 8:47AM
and all this time I thought the weather in China determined if I was going to get lights justice off of prince.
macanima Apr 30th 2008 9:57AM
It's called the gambler's fallacy. It's fairly pervasive not just among WoW players but among people in general - the believe that if I have a 1 in 3 chance of (X) if I do (Y), then if I do (Y) three times, I am guaranteed (X).
kellzea Apr 30th 2008 2:20PM
reply to TK, im dislexic, so thank you for attacking a disability in a public thread nothing to do with what my disability affects.
also, you understood what i meant, so why try a cheep shot because your to stupid to realise that spelling doesnt have to acurate, but maths does,
DIAF
kellzea Apr 30th 2008 3:29PM
i think alot of people miss the fact that drop rates secure the "theoretical average" over the whole population of a server, if not the entire world of servers.
"MACE OF YOUR QUEST" drops from "EVIL BOG MAN THING ONE" a theoretical 10% of the time. but your drop rate although still 10% may look more like 99% or 0.0001%.
a nice way to put this is
if you roll one million dice one million times you will get very nice and near stat averages, but each individual dice may have rolled one million ones (any warhammer players will agree to this).
you are simply a die. your may never drop, your mate billy might get them everytime.
proability is a biatch
so is TK
Sl0th Apr 30th 2008 5:02PM
Ah, the RNG. my mortal enemy. You can't influence it, you can't beat it, you can't bend it to your will... You can only sit back and watch it mock you. I mean, four weeks in a row of Idol of the White Stag from Supremus. Really? You're giving us an idol over and over that our druids are only taking grudgingly in case Blizzard changes it some day? And you're not going to drop multiple Choker of Endless Nightmares or at least another Brutalizer for our new main tank. And don't get me started on how many times back when we were running him weekly old Gruul dropped his comb, er, his Axe of the Gronn Lords when just a single Dragonspine Trophy would have really brightened the days of so many of us. The only DSTs in the guild are on the persons of new members who weren't effected by our curse.