> "Instead, Google says its ad-buying tools will use new technologies it has been developing with others in what it calls a “privacy sandbox” to target ads without collecting information about individuals from multiple websites. One such technology analyzes users’ browsing habits on their own devices, and allows advertisers to target aggregated groups of users with similar interests, or “cohorts,” rather than individual users."

I'm having a hard time parsing this out, and seeing what's actually changed. How do they determine an individual's "cohort(s)", without collecting information about that individual across multiple websites?

Is it simply that the data is collected and processed client-side, rather than server-side? Would using a non-Chrome browser effectively opt-out altogether, then? I find this difficult to believe.

The idea is that they group you with N other similar people where N is large enough to anonymise you enough to stop the worst complaints but small enough that advertisers still find it useful.

Some sort of principal component analysis to determine your "cohort".

An advertiser isn't that interested that you are you. They care that you are, for example, 55 with an interest in gardening and have been looking at lawnmower review sites.

So if I look up the specs on a pair of Bose QC-35's, I won't get internet-stalked with ads for that specific pair of headphones for the next 3 weeks whenever I pull up a weather report? But in stead I may see an uptick in general audiophile ads if I'm constantly reading articles about new gear that comes out? At least that sounds like a partial win in my book -- the first case was too creepy because it was so blatant. The second one may be worse because it is more subtle, but it creeps me out less for some reason. Kind of like how 2-3 decades ago when computer magazines were a thing, I kind of expected ads for computer parts in those magazines.

Edit: Actually, come to think about it, I wonder how people would have felt in the 80's if they got one of several editions of a newspaper based on magazines that they also subscribed to. Households that subscribed to fitness magazines would get a newspaper with more gym membership and weightlifting gear ads, and households that received woodworking magazines would have more Craftsman ads in their newspaper. Would people appreciate the customization of the paper, or would they see it as an invasion of privacy?

The WSJ seems to be describing https://github.com/WICG/floc, but the kind of remarketing you're describing is what https://github.com/WICG/turtledove is intended to support. Advertisers would still be able to run that kind of personalized ad, but the browser API would not allow them to learn your browsing history in the process.

(Disclosure: I work on ads and Google, speaking only for myself)