Better understanding of drop rates. Equation/Algorithm inclu

[BestRAmarEver]

As we all know. A drop rate of 1/2 means that when you kill 1 enemy you have a 50% chance of the item dropping.

The question arises though, what are the chances if you kill 100 enemies at a 1/2 drop rate? Obviously it can't still be a 50% that you get the item ONCE.

A better way to illustrate this is to flip a coin. Each time you flip it you have a 50% chance of it landing on heads... but as stated before, obviously if you flip a coin 100 times you don't have a 50% chance of it landing on heads only once.

I know there is an equation/algorithm that lets you know how much your odds increase each time you kill an enemy. In fact it was posted on PSO WORLD a year or so ago, but I can't seem to find it anywhere.

Does anyone know the equation for this?



<font size=-1>[ This Message was edited by: BestRAmarEver on 2006-04-05 12:50 ]</font>

[Tact]

Using the basic laws of probability, it can be said that you are more likely to get the item after the first time, but the chance is still 1/2.

Example: You kill a Pal Rappy, looking for its Red Scorpio. It drops a Dimate instead, with a 1/2 chance that it drops the gun. An hour later, you do some piping and find another Pal Rappy. You only have a 1/4 chance of NOT getting the Scorpio because you multiply the droprates. 1/2 times 1/2 = 1/4. However, I'm not sure if this applies to higher drop rates.

[Saraphim]

I may be wrong, but I thought the 1/2 rate (as an example) was on top of the drop anything rate.

Let's use the Pal Rappy example again. You kill a Pal Rappy, and it drops nothing (idk what the drop anything rate is, but we will use 99/100 for now), so the 1/2 Red Scorpio rate is meaningless on that enemy. The next Pal Rappy you kill drops 2,000 meseta, so now the 1/2 rate applies.

This is somewhat like the Parasitic Gene "Flow" drop. I believe it's a 1/49 drop, but the drop anything rate is 0.

Just thought I'd mention this little aspect of drop rates. If I am wrong, please let me know. http://www.pso-world.com/images/phpbb/icons/smiles/icon_smile.gif

[Skorpius]

No, you're thinking about it wrong.

1/2 is the probability for one trial. If you multiplay it by 100, you'll get what?

Since 1/2 is a fraction, what is its decimal? .5, right? So what happens when you multiply 100 by .5?

You get 50.
50 hits out of 100 trials. Which can be reduced to 1/2.

[Vire]

How would this apply to different numbers, if it does?

[OdinTyler]

Long story short, the fraction applies to each enemy. After the kill, if the desired item isn't dropped, the probability ratio starts anew. If say something has a 1/200 droprate, if it doesn't drop the item, the next enemy will also have that 1/200 droprate. It won't go up & down. It's all a matter of chance or roll of the die. The droprates blow (as we can agree), but, they are what they are.

[Saraphim]

On 2006-04-04 20:06, OdinTyler wrote:
Long story short, the fraction applies to each enemy. After the kill, if the desired item isn't dropped, the probability ratio starts anew. If say something has a 1/200 droprate, if it doesn't drop the item, the next enemy will also have that 1/200 droprate. It won't go up & down. It's all a matter of chance or roll of the die. The droprates blow (as we can agree), but, they are what they are.



So then the "drop anything rate" really doesn't affect the chance of a rare drop huh? Guess that's a good thing http://www.pso-world.com/images/phpbb/icons/smiles/icon_smile.gif

[Dhylec]

Saraphim wrote:
So then the "drop anything rate" really doesn't affect the chance of a rare drop huh? Guess that's a good thing http://www.pso-world.com/images/phpbb/icons/smiles/icon_smile.gif

Yes & no.
For normal enemies, the drop rates should have been included the DAR.

Rare enemies have that extra 1/512 appearance rate in addition to the DAR. But since rare monsters have 100% DAR, it's doesn't really matter then. ;]

[FayteEternal]

So in my case with the Heaven Punisher having, what, 1/190,000 (Ultimate Caves/Yellowboze) drop rate, it doesn't matter I've killed thousands of Crimson Assassins it seems but each one's probability is reset individually to 1/190,000+? O.o!
I may give up this hunt..................which pains me because I really want this gun.

[Saraphim]

On 2006-04-04 20:42, Dhylec wrote:


Saraphim wrote:
So then the "drop anything rate" really doesn't affect the chance of a rare drop huh? Guess that's a good thing http://www.pso-world.com/images/phpbb/icons/smiles/icon_smile.gif

Yes & no.
For normal enemies, the drop rates should have been included the DAR.

Rare enemies have that extra 1/512 appearance rate in addition to the DAR. But since rare monsters have 100% DAR, it's doesn't really matter then. ;]



I can remember at least once a Del Rappy didn't drop anything. No meseta or anything. Is that because it's BB, or am I on drugs http://www.pso-world.com/images/phpbb/icons/smiles/icon_razz.gif (and no, I'm not!)

[Mixfortune]

There's a difference between the probability of the drop and the odds of getting that result once after a certain amount of trails.

Basically, the answer for "what are the chances you'll roll a dice 10 times and not get a 6" will be different for "what are the chances you'll roll a dice and get 6". It's a different kind of trial, with a different kind of result. And that's where algorithms come in. It's not just a simple fraction for the first.

The OP may want to simply search around for probability and algorithms, maybe something about cumulative success rates, etc. That might be more useful and faster than on the forums here, since it could be applied to both the PSO situation as well as others.

[Skorpius]

Or just look into simple algebra, since it's mostly cross-multiplying fractions and variables.

1/droprate * X/Trials

[Cryo_]

This is pure statistics.

p = probability and n = number of times you'll do the experiment (in this case, kill the enemy)

the chance you'll find the item on the n'th time is: (1-p)^(n-1) * p
meaning behind this: you have to fail n-1 times and succeed the n'th time

Now if you do n experiments and you want to know what the total probability is:
the chance you'll find the item on the 1st time + the chance.. 2nd time + ......... + the chance n'th time
= 1 - you fail n times
= 1 - (1-p)^n

So far the math lesson for today http://www.pso-world.com/images/phpbb/icons/smiles/icon_smile.gif.

[GrumblyStuff]

On 2006-04-04 19:16, Skorpius wrote:
1/2 is the probability for one trial.

Since 1/2 is a fraction, what is its decimal? .5, right? So what happens when you multiply 100 by .5?

You get 50.
50 hits out of 100 trials. Which can be reduced to 1/2.
Say that to the 17,716 Gillchics I've destroyed so far. You'd think I'd have that S-Parts 2.01 some time after run 103-104 of Unsealed Door but I'm shooting past 172.

[ulyoth]

I always just think of a wheel like in wheel of furtune. Kill an enemy you earn a spin, taking the 1/190,000 drop rate there would be 190,000 sections and the pointer would land on 1 of them. Kill it again and you wuld get another spin. I wonder though, does the game calculate whether you get a rare first? or does it "spin" XP for normal items first?

[Neith]

As far as I know, drop anything rates are considered when droprates for rares are calculated.

For example, Melqueeks are known notoriously for having a very low DAR (15% If i remember).

The droprate for an 11* weapon without taking the DAR into consideration is something like 1/10,083. Since Melqueeks only drop anything 15% of the time, you divide this figure by 0.15.

This gives you a total of 67220. This is why Yasha's droprate from a Melqueek is 1/67,217 (allowing for rounding etc). Anyone, correct me if I'm wrong ;o

Another example, again using an 11* weapon. Sealed J-Sword from Gi Gue. (lol, using my hunts as examples). Take standard 11* weapon droprate, and divide by Gi Gue's drop-anything rate (which is quite high- 80% I think). 10,083/0.80= 12,603.75, rounded to 12,604. Look at the SJS droprate, and you'll find it's 1/12,604.

I 'think' that's how it works- seems to work out nicely anyway. Someone correct me if I'm wrong.

[OdinTyler]

And who says you can't use math in real life after school? LOL

[Zarbolord]

I hate stats and prob, but I'll still answer. I think it's the reset thing that confuses people. It's as if nothing happened before, as if you never saw that enemy until then, the drops then stay the same rate. Meaning that anything you're looking for won't drop easily, you might search forever and NEVER find what you're looking for. You could also find it all the time, but it only happens when the drop rate dice hits the denominater.

[BestRAmarEver]

Thanks for the help guys, and the guide was actually still here... I had someone from the PSOBB boards give me the link.

http://www.pso-world.com/sections.php?op=viewarticle&artid=2294

It's nice to know that at SOME point the item will eventually drop. >:D

[FayteEternal]

Every MMO out there has those all-important items that we'd like to have. So many factors play into your chances of getting those items. While we stress and groan over sadistically absurd drop rates (like me with Heaven Punisher), we should count our blessings that aside from poor drop rate %'s, the majority of PSO's super rare items can be obtained by soloing (for the most part) whereas many super rare items in other games (like FFXI) require 20-64 people to kill the NM's (bosses) to get (Yes, those numbers aren't typo's). And even then more times than not the all-important item doesn't even drop!!^^;;;
I really have no idea why I mentioned that, just food for thought I guess. lol.

[A2K]

The rates are a lot better than Dreamcast Version 2's, in any case. You never will find anything but Red Handguns and Ancient Sabers in Ultimate there (maybe the occasional Imperial Pick if you're lucky). Some weapons have apparently have rates beyond 1 million to one, even.

'Course the game was imbalanced in a lot of other ways back then, too. We all still loved it anyway, though. The game just hasn't been as popular since then...