The count of contributions (summary of Pull Requests, opened issues and commits) to public repos at GitHub.com from Sun, 30 Aug 2015 10:08:52 GMT till Tue, 30 Aug 2016 10:08:52 GMT.
Only first 1000 GitHub users according to the count of followers are taken. This is because of limitations of GitHub search. Sorting algo in pseudocode:
githubUsers
.filter(user => user.followers > 1)