I've never been one for conspiracy theories, however Adsense does seem to exhibit some peculiar behaviors.
Along with a few others here, I experienced a decline in revenue a couple of months ago - the reason of which was unknown (but that isn't what this thread is about).
To try and combat this, I've done lots of testing on my sites and found a new ad position which improved CTR by ~20%, which is considerable. (Before someone jumps in here, 20% increase means x * 1.2, not x + 20 as some seem to use!?).
After rolling this out, the site earnings went up quite a bit. However, a couple of days after this, my earnings are the same as before! This site is still performing better relative to before, it is just the other sites that are doing worse. I've not changed a thing on them.
It is almost like the revenue has been pre-determined, as any improvement does not always increase the overall revenue. Of course, if I double or half the impressions there will be a difference - however increasing the CTR on one site doesn't do much.
I would have assumed this change would have provided a big increase in revenue, and in the past this would have been the case.
Although these comments are based on pageviews in the millions, so I would consider them statistically relevant.
Has anyone else experienced this, or have any comments on the matter?