Likes, anger emojis and RSVPs: the math behind Facebook's News Feed — and how it backfired

In late 2017, Facebook had a big problem: users were commenting on, "liking" and resharing posts less than they had in the past.

The declines in engagement, visualized in charts on an internal document viewed by CNN Business, looked like wiggly black-and-blue frowns. Facebook decided to make a change — and fast.

That December, other internal documents show, the company quickly came up with a plan: it would refocus its News Feed algorithm on a new metric it referred to as "meaningful social interactions", or MSI, for ranking people's interactions on Facebook. MSI would assign different point values to things such as "likes" and comments on posts, and even RSVPs to events, and take into consideration the relationships between people, such as that of a person writing a post and a person commenting on it. It launched in early 2018, marking a new era in the ways the social network monitors and manipulates its users, and experiments on their data.