Adsense patterns with changes

[dmz17]

I've been running adsense on a few sites for almost a year now. Generally happy with it (reporting could be better), and cognizant of ups and downs in revenue. However, there is one noticeable pattern I can't explain and am curious if anyone has any hypotheses.

It seems that every time I make an Adsense improvement (a change that results in an increase in earnings), the percentage increase dwindles after an initial surge. Most recent example was switching from leaderboard to skyscraper ad layout. There was a noticeable initial increase, then it settled down to almost the level prior to the switch. Similar experience when launching large chunks of new content. The impressions and earnings go up, then the effective CPM goes down.

Any insights of Adsense's workings or visitor behavior that might explain it?

[HeIp]

This is due to people getting used to the ad format.

At first your users will not notice that they are actual adsense ads and will click on them more and as they learn they are ads the ctr will go back to the regual level.

You are very smart to change the styles around as this does help alot with ctr and earning money.

Just like wal-mart everytime you walk into the store you see something different and you always look at what it is. If you keep the same formate everyday on your website your regular users won't even look at your ads.

Hope this helps you, also if you have any help for my post please let me know as I am really in need of help.

Thanks,
Stephen

[Never_again]

HeIp has it right on the most likely reason. Returning visitor see something new and it attracts them. They click. CTR goes up. But, after some time, it is no longer new and they become "blind" to the ads which causes your CTR to move back down.