Hi Jonathan, thanks for asking! I think there are several possible definitions for what it might mean to leave:

- hedge bets by setting up an account elsewhere as a reader

- set up an account elsewhere and cross-post

- stop using your account and not transferring elsewhere

- stop using your account and move elsewhere

- delete your account, and either move elsewhere or not

Twitter isn't very transparent, so it's not easy to know what the numbers have been on Twitter's side, but we do have evidence of growth in millions of active user accounts on Mastodon. For a clearer picture just of Twitter, we'll have to wait to see what the trends are on ComScore and other independent metrics creators once they settle down. https://absolutelymaybe.plos.org/2022/12/05/mastodon-growth-numbers-might-not-mean-what-you-think-they-mean/