Google has made some adjustments to how it uses referral URLs for contextual matching of AdSense ads. Google has started expanding the use of query words in referral URLs to a few hours.

Basically what this means is that Google is using user's search history to determine what ads to show on sites using AdSense. If a user arrives at one AdSense site via a search results page, and then goes to another AdSense site within a few hours, they might see ads based on the referral data from the first one.

"The technical way that we're doing this is by associating the relevant query words in the referral URL with the existing advertising cookie on the user's browser," says AdSense Associate Product Manager Rebecca Illowsky. "After a short period of time (a few hours) the query words are no longer used for the purposes of matching ads. Of course, users can continue to opt out of our advertising cookie at any time here."

"This allows us to deliver more relevant ads on a wider range of AdSense partner sites that a user may browse over the course of a few hours," she adds. "Using signals from the referral URL is just one part of our teams' continuing efforts to deliver even better contextually matched ads on your website."

Some people claim to have already seen a rise in clickthrough rate since Google made these changes. Commenting on Google's explanation, one reader says, "I saw a rise in CTR and was wondering [if] something was cooking so I guess this was it."

Have you seen a rise in AdSense CTR recently? Let us know.