I currently have 4177 ecology knowledge which should equal to an extra drop rate chance of 12%, and I firmly believe my drop rate has decreased.

Prior to 4k knowledge, when farming helms I would average around 16 heve helms and 16 forbidden books an hour. Immediately after i hit 4k, I have entire hours with no book drops and less than 5 heve helms, which never happened before. Even with a level 10 node and a drop scroll, I'm seeing very few drops.

I understand bias and chance as being just that, a chance, but to see such a significant and consistent drop rate over such an extended period immediately after hitting 4k makes me question the effect. 

Has anyone else experienced something similar to this?

for me lvling a node gets me less drops i had cadrys at 8 for a long while farming there and pretty much wouldnt get any ancient scrolls with a drop scroll even while the 50% drop rate buff event was going on + kama blessing and yea no scrolls for 1800 mobs for guild mission typically i drop it down to lvl 1 and in an hour with just a drop scroll I get 3 yona frags 5 scrolls and several +12-13 peices +ruby/blue rings for crafting the cadry ring. So yea definitely know that the stuff that supposedly increases drops does the opposite in some cases 

You cannot datamine these statistics with the amount of grinding time you have available.  You may have a .001% chance base so 50%+12% would be .00162 which isn't much difference.  Statistically you would have to grind 100,000 mobs or more to get a full data sample.

Hi everyone!

You must remember that Pearl Abyss are continously changing drop rates. They adjust drops rates to the number of players, market prices and for the general balance of the game. At the begining the drop rates was wealthy due to they wanted you to stay playing all the time. Now they adjust it to the normal rates. Basicly they do what they want. Hehehe. So don't bother trying to change it or complaining and just have fun and play. I told you friendly but my english is bad. I apologyze.