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Here's why. Many times, the robot is set to follow the INDEX, FOLLOW rule, which means basically index *this* page you are looking at and then follow all the clicks on this page to other pages on the site.
iPowerWeb has a marketing solution it offers to its customers that does this every 30 or 45 days. The way to *fix* this is: add a meta tag to the head section of your page that indicates INDEX, NO FOLLOW.
That way, every single link on your page won't be clicked (say in a matter of seconds which probably sets off some type of warning bells at Google) and you will be less liekly to be charged with fraudulent clicks.
This happened to my site.
What I am concerned about for my site is that the CTR averages are not very average over the period of a month or so. I find that I may have a steady (+/- .25) rate for 15 days and then have it drop all of a sudden for the rest of the month. This really bites. It doesn't allow businesses to plan well on income from advertising... even for the same number of impressions and clicks. I realize this has to do with their other program and the cost bid per click. Still i wonder sometimes whether the ability to have more time for content is really worth it for the hassle of the wild swings in weekly averages. Just when I think I have a handle on the days and returns, it all goes to hell.
Futhermore, adding an INDEX, NOFOLLOW robots meta-tag would prevent spiders from following your own internal and external links as well, and may not even apply to any content in a frame.
""3. Why do I detect a different number of impressions than what shows in my reports?
We count impressions only when our ad code is executed by a user's browser. There are therefore several factors that would cause a discrepancy between the impressions you register and the impressions listed in your AdSense account. Instances that wouldn't execute the code include:
Other spiders, robots, crawlers from other search engines
Browsers that don't support the <iframe> tag
Programs that people may have written to grab website content