They do A/B testing. https://meta.wikimedia.org/wiki/Fundraising_2010/Banner_testing https://meta.wikimedia.org/wiki/Fundraising_2010/Banner_test... https://d

They do A/B testing. https://meta.wikimedia.org/wiki/Fundraising_2010/Banner_testing https://meta.wikimedia.org/wiki/Fundraising_2010/Banner_test... https://diff.wikimedia.org/2013/04/08/intro-to-the-statistics-of-ab-testing-with-wikimedia-fundraising-banners/ https://diff.wikimedia.org/2013/04/08/intro-to-the-statistic...