I know most of you will reply saying that its the page content ... I understand that ... But for some pages I see that even though the page is content heavy and should have displayed content specific ads .. but the ads displayed was based on the site content.. for eg: if you have a hawaii travel based site .. and on that site u have a page which deals just with american idol and not a single word related to hawaii ... still hawaii ads are shown on the american idol page ... On another site which has pages on a niche with not much ads ... if I have the american idol page I see american idol ads being displayed ... somewhere in the google adsense logic .. IMO it requires some tweaking...
I see a mix of both, if google cant find anything related to the page it shows something about the site topic.
I would say 1st it checks for the keywords in site content and site url and then it checks for the keywords in page content. So the ratio is more of site then of page. But once the page is indexed it would page content which decides the ads in the box. If it has ads related to page content it would place it otherwise it would go for ads on site content. It simple logic i guess.
If you read the AdSense patent carefully you'll see it mentions it looks at the topic of "related" pages as guides for what to place on the content and defines a "related" page as being a page in the same folder, on the same site, linked to, linked from... lots of details, actually.
I can tell you it's been domain related in my experience. I have three subdomains setup on very different subjects but I keep getting adverts on my two less popular (and much newer) subdomains that are completely wrong for the "site" content. They are targeted at the content of the other much more popular (and older ) subdomain. Very annoying to be honest as 70% of the advertising being displayed on the site are completely irrelevant to the users that are browsing the site..
I think content of page gets pereference to site. I got few pages on my site which are totally unrelated to my site and it is on these pages that I have placed the adsense ads. I always get ads according to page content. Earlier when I used 3 ad units , sometimes I had 1 out of 12 ads related to my actual site theme. Now I use only 1 ad unit and I get only ads related to page's content.
Are you linking the other two sites to your older site? Then AdSense would be assuming they are related. One tactic you can try is to link your other sites to authoritative external sites on the "real" topics. For example, link to specific pages in the Wikipedia. You can also either remove the links to your other site or remove them from consideration by using the site targeting feature's "ignore" syntax to hide them from AdSense.
My older subdomain links to the new subdomain because it's a PR4 and the new sites can get all the help they can get.. My new subdomains however don't link back to the main site at all.. Would having a link from the old sub-d to the new sub-ds be the cause do you think? [Edit]Oh and the new sites have a lot of links to relevant pages online.. Apart from co-op links at the bottom of the pages that's all they have.[/Edit]
Indeed, look at claims 11, 12 and 13 of the patent: Claims 12 and 13 (and 14) expand upon claim 11. Claim 12 says document A is similar to document B if A links to B. Claim 13 says document A is similar to document B is B links to A. So yes, the links to the site from outside can have an impact.