I haven't been contacted by Adsense but I have a proven method (at least in the past) to increase earnings 40% on certain types of sites. So this is a tip Adsense. For smaller, niche, sites please allow Webmasters to disable CPM ads. We may all make a lot more earnings (Google included)
I still firmly believe that for smaller sites, say 50,000 page views a month, (niche type sites) Pay per clicks (PPC) ads produce substantially more earnings than CPM ads.
At the link above you can see my stats.
On August 16th, 2006 I asked Adsense to discontinue CPM ads for my account and they promptly did so. The change occurred on the 18th, And WOW:
For periods of 10, 30, and almost 60 days before and after this change, EARNINGS after Aug 18th are consistently UP approximately 40%.
Unfortunately for me when Adsense implemented "third party ads" a couple years back it appears at least for me the disabling of CPM ads has been removed. (You had to send Adsense an email request for this change) Since this was a phased in change I can't say whether I had a 40% decline after CPM ads were reinstated.
It does appear that sometime in the last two years or so Adsense managed to increase the eCPM of CPM ads substantially, but even today on low traffic pages PPC ads outperform CPM ads for overall earnings.
How can I tell. I have URL channels for many pages. I sort the results by eCPM. You will see eCPM amounts where there are no clicks at all for some pages. These URL channels are obviously only producing earnings due to CPM ads. If the earnings for CPM ads were competitive the URL channels showing clicks would be somewhat randomly interspersed with URL channels showing earnings without clicks. This is not the case, eCPM is almost always higher for the channels that received clicks! Oddly enough just for reference when you do this eCPM sort, the remaining channels that have no earnings whatsoever, but have impressions, are shown in reverse alphabetical order. Why is this oddity important to know? Because you will see URL channels with zero eCPM, but they are producing earnings!
What? Yep, I'm whispering; using this knowledge one can detect eCPM's less than 0.33 cents. Yes that's 0.0033 dollars.
I will say however that somewhere in the last two years Adsense has made CPM ad rates more competitive so I don't know that I see rates this ridiculously low any more.
So I would love to have Adsense review my sites data 10,30,60 days before and after August 18th, 2006, THEN I would love to have Adsense perform the same 60 day test today (disabling CPM ads for 60 days or so) then review the site in question's earnings! Why may CPM ads be a problem for some sites?
Adsense has a huge inventory of CPM ads to show and this is great for high traffic web pages. But these high traffic pages must dwarf the earnings data for the same CPM ad showing on a low traffic niche page. Why does this matter? Because the CPM ads displace the better performing PPC ads (again for lower traffic, niche sites).
If a CPM ad is showing, a PPC ad is not!
I have numerous low traffic, content intent, instructional pages that might not earn even a penny for a weeks CPM impressions. But if there are PPC ads, one click can be 1,2,3,4,5,6 even 7 dollars! It would takes thousands of CPM impressions to earn that much.
This is a statistical variance problem Adsense has not, and probably cannot account for; trying to compare bids for the same ad for a very high traffic page versus a low traffic page.
Only the test I describe can do it, and the test requires Adsense to stop CPM ads for a period of at least a month for many low traffic pages.
Wow well this got to be quite a post. But dear Adsense wouldn't you like to be earning 20 to 40% more on low traffic niche sites? To save a lot of work please think about a CPM ad on/off switch, restoring control to Webmasters.
Adsense could then quickly acquire statistical data, monitoring Webmasters performing this experiment!
I doubt this will be done, only because major Advertisers want to blast "branding" ads all over the internet and Adsense still makes this service too cheap! It's not likely a person visiting a page about "repairing hot water heat widgets" is going to click on an Giant Insurance Company ad, but remember this ad is displacing the PPC ads! The earnings Adsense is missing is peanuts, but I'd like to have some of those peanuts Adsense is dropping!