There are only a few ways to get a truly even distribution. There are many more ways to get an uneven distribution. So you should have an uneven distribution on the vast majority of raids.

An example: let's say you get 6 drops in total. To have an even distribution (one of each), the first pick doesn't matter: 1. The second pick can't be the one you already had, but there are 5 other possible picks: 5/6. The 3rd pick must be one of the remaining 4: 4/6. Etc, etc. The last pick has only 1 valid pick to get an even distribution, so this already cuts your chance in 6: 1/6.

So the total chance is 1 * 5/6 * 4/6 * 3/6 * 2/6 * 1/6 = 1.5% chance to get a proportional distribution for 6 drops.

PS. Like I explained in another thread, it is a common mistake to equate randomness with proportionality. For small samples (like you see in the game), proportional results are actually very unlikely if the game is truly random.

Last edited: Aug 18, 2015