AdSense Dependant and Independant Variables

Oh man this is a head screwer!

For a while now I have been tracking two things which have a strong impact on my adsense earnings for any given adsense impression: How many pages a visitor has seen on my site and what site referred them to my site.

Now I've been treating these variables as independant which means I have tracked them seperately assuming no interplay between the way these two variables impact my adsense clicks. This is moronic the variables couldn't be more strongly tied together if the hypothesis I have for "why" google referred visitors have higher CTRs than non Google:

A google visitor sees adsense ads relevant to the search term they typed in google hence is more likely to click

If the first reason holds true then browsing through my site it is clear that the ads on the "paper blimp" page are v. different from the ads on the paper airplanes homepage. It would then also hold true that:

The further a Google visitor is from their page of entry the less correlated the adsense ads are to their keyword of entry

If this holds true you would expect the drop off in the ctr for a google user to be far greater from the first page viewed to 4th page viewed than for a non google user. The good news is I can test this and see if these variables are independant and whether I should treat them as such but the bad news is I can't kick this off until after eBay Live due to my commitments over the next month.