Quoting from the AdWords Help Center with italics added by me:
[...] Quality Score for the content network is based on the following factors:* The relevance of the ad and the keywords in the ad group to a content page
* The ad's performance history on the page and similar pages
*The quality of your ad's landing page [...]
Excerpted from:
Quality Score for the content network
[adwords.google.com...]
Which links to more information here:
Is a Quality Score calculated for my contextually-targeted ads?
[adwords.google.com...]
AWA
I know it's not the same on search and content, but it's a good indicator b/c Google is very sneaky with their quality score algorithm, especially on the content network.