The options is in your AdSense control panel under MY ACCOUNT - ACCOUNT SETTINGS - "Interest-based Ads Preference"

Thanks, you're right. Haven't been in there in a while.
It seems they don't just use the visitor's ad clicks on YOUR site (which wouldn't be so bad), as they allude to in one place, but those on ANY other site they've been to. In fact, from my experience, since I NEVER click on google ads (just to be safe), they don't JUST use ad clicks to determine ads on your site, but also searches and/or what other sites they've been to.

I suppose that we can't turn off interest based ads: we can only stop transfer the information from our sites. Am I wrong?

Read my post, you can disable them on your site!

When interest based first came out, the word was that we could only disable the collection of information on our sites for use in interest based displays. (ie we could only turn off whether our visitors were tracked while on our site)
But the way the interface is worded certainly implies that the publisher can now turn display off and on.
(and once again - Adsense has set it up for the account, not per site *sigh*)

leadegroot, interesting supposition, but I'm afraid that this rule: " Even if you choose to opt out of displaying ads based on interest categories, your site(s) will continue to show ads based on user interactions with an advertiser, such as visits to advertiser sites." is still acting. (:

Is it possible to turn off "interest based" ads?

The adsense Help page [google.com] says:

You can opt out of showing ads

that are based on user interest categories (e.g. 'sports enthusiasts'). In turn, Google will not use visitation information from your sites to help create interest categories. However,

you cannot opt out of showing ads

to users based on their previous interactions with the advertiser, such as visits to an advertiser's website.

[bolding in the above quote added by me]

It's just marketing spin to say "previous interactions" isn't the same as "interest based" in this case.

The weird stuff in the adsense help was pointed out when the program started, but never cleared up AFAIK.

As a result the action one can take in the settings is still quite unclear as to what effect it will (or will not) have.

" Even if you choose to opt out of displaying ads based on interest categories, your site(s) will continue to show ads based on user interactions with an advertiser, such as visits to advertiser sites."

It makes sense to track interaction with advertisers relative to your site regardless.

For instance, how many times should one person be allowed to see and click the same ad before AdSense stops showing that ad to avoid competitors of emptying an ad budget?

Also, if you keep showing the same visitor the same ads and they keep ignoring them you want to show them something new, so interaction with the advertisers or lack thereof is necessary to keep your surfers clicking.

I wouldn't mind if they only took into account other interactions on MY published website, but if they take into account something the person responded to on other, relatively unrelated websites (which from my experiences is happening), then it simply may be way un-related and even confusing. For instance if they are from New York, and look for restaurants on Monday to go out for the evening near home, and then on Wednesday decide to look for dining options near their vacation to Disneyworld in Florida next month, on a different travel related website, should they really still be seeing ads for restaurants in New York?

BTW, it's still a lot early to make a scientific observation, and could just be coincidence, but jut since I turned it off, less than 24 hours ago, our eCPM and earnings shot back up 20% almost to where it was a couple months ago.