dnx134 - 9:42 am on Mar 8, 2007 (gmt 0)

It's my belief that Google have some kind of 'rating' system for publishers in place, based on a number of factors including the perceived 'quality' of your sites and the length of time you've been in the AdSense program, and that the percentage Google pays you is based on this rating.

As an example, I've had reason to move a high traffic site from one AdSense login to another, and did this simply by chaning the publisher ID in the ad code. Nothing else changed.

Overnight, average EPC jumped 500%. Impressions and clicks remained the same, only the amount I was earning per click changed. Now it could be argued that changing the publisher ID forced Googlebot to re-look at the content of the pages, but this was an established site and the advertisers did not change noticeably.

Over time, earnings gradually declined back to previous levels, which is what leads me to believe your 'rating' is at least in part based on how old your account is. For the average user it won't be noticeable, but it looks to me like new users are given an encouragingly high percentage of revenue which gradually decreases over time - forcing you to work harder if you want to maintain - or increase - your earnings.

Of course, Google can handily hide behind the fact that they refuse to tell publishers how much they pay, which is franky ridiculous. I think it will probably take a legal challenge to get Google to reveal how it calculates publishers earnings before we'll ever know - and that's not likely to happen because people are scared of losing their accounts and livelihoods if they challenge Google.