Once a change like Tas’ has been tested on each of these audiences, he’ll present the resulting data at one of the news feed team’s weekly “ranking meetings” and field a volley questions from colleagues as to its effect on various metrics. If the team is satisfied that the change is a positive one, free of unintended consequences, the engineers in charge of the code on the iOS, Android, and Web teams will gradually roll it out to the public at large.
Even then, Facebook can’t be sure that the change won’t have some subtle, longer-term effect that it had failed to anticipate. To guard against this, it maintains a “holdout group”—a small proportion of users who don’t see the change for weeks or months after the rest of us
It’s like the 10th Man from World War Z!
Essay about how Facebook shapes the feed. I keep mine set to “Most Recent” and kid myself that I am in control. Ha, ha!