Question about Cohort ID in FLoC

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高橋球

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Aug 13, 2021, 5:54:51 PMAug 13
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Hi! I have two questions about FLoC. 

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 Q1:
Will the meaning of the Cohort ID change at some point? 
For example, passage of time, when the Cohort ID is recalculated etc...

Q2:
Will all browsers recalculate and change cohort IDs at the same time?
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Thanks, 

Sam Dutton

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Aug 16, 2021, 7:00:31 AMAug 16
to blink-dev, kyu.ta...@d2c.co.jp
Hi!

The answers below are in relation to the initial version of FLoC. The origin trial for this is now closed.


> Will the meaning of the Cohort ID change at some point? 

Not for the same version of the FLoC algorithm. FLoC calculates the browser's cohort ID based on recent browsing activity. Browsing activity for a user is likely change over time, but the meaning of a cohort ID (for a cohort version) doesn't change, since it represents a grouping of browsing activity in 'FLoC space' for that version of the FLoC algorithm.

That's why document.interestCohort() provides a version (such as chrome 2.1) as well as an id (such as 14159). You can think of this as a two-part cohort identifier.


> Will all browsers recalculate and change cohort IDs at the same time?

Browsers that implement FLoC compute the browser's cohort ID on the user's device, based on recent browsing activity. The only factor affecting the ID computation is the user's recent browsing activity (assuming there is no algorithm version change). The browser recalculates its cohort ID periodically, on the user's device. That recalculation may or may not coincide with recalculation by other users' browsers, but there is no sharing of individual browsing data with the browser vendor or anyone else.

Regards

Sam
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