While Adsense has fairly detailed reporting, it provides no information in this area. But with a little bit of work, it turns out to be pretty darn easy for you to collect this data ... and the results might surprise you.
But you can specify an alternate PSA so that an image ad of your chice is displayed, and when the surfer clicks on it, they go to your URL. I happened to be interested in this because I wanted to highlight/support a charity of my own in the v7ndotcom elursrebmem SEO contest ... but you can certainly send people to a commercial page or whatever. Remember this is only done when a PSA is going to be displayed anyway, which does not generate any income at all. Ironically, I have not found any way to "force" a PSA to show up ... but after you have this in place, you'll know which pages show PSA's and how frequent.
1. I created the following file as
http://psa.watching-paint-dry.com/adsense/psa-728x90.html:
2. I then created a 728x90 image which looks as follows:
3. I added the following line to the .htaccess file in the "adsense" directory.
This is really a "bonus" step that allows you to track each seperate
image ad size - consider it analogous to an Adsense channel as outlined
in the results section.
4. You can test all of the above by hitting the URL in step #1. You should
see the image in step #2 show up, and when you click on it, get a new
window as specified in the code section of step #1. Now you are ready
to go live.
Add the following line to your Adsense code - doesn't matter where - after the google_ad_client is as good as any. Note that it doesn't matter
if you have the Adsense javascript embedded in your html or as part of
an included .js file.
google_alternate_ad_url = "http://psa.watching-paint-dry.com/adsense/psa-728x90.html"
Remember to changes the pathnames in all of the steps to make it specific to your domain,
image size, etc.
Compare to the total hits on the web page and you know the percentage of PSA's. Plus you'll be able to identify those pages that have a higher percentage of PSA's and perhaps tweak them so Google can beter determine relevence.
Oh yeah, what is the point of step #3? Every problem in computer science can be solved by another level of indirection, and that is basically all we are doing. If you have another image format (or another channel), then optionally change the filenames slightly to match that. The final landing page will be the same (assuming you want that), but you will have log data that allows you determine what page the user saw the PSA on and clicked thru from.
The next two days, the percentage of PSA's were about 0.5% ... and about a third of those were coming from one page that I'll have to take a look at - not sure why is seems to be "stuck" displaying PSA's. But none of this I would have otherwise known. All of the above data is based on a web site getting >100,000 impressions/month, so it's semi-reasonably statistically significant - even more interesting would be a web site getting >100,000 impressions/day.