Design a system to predict which users will attend Facebook events in the real-world?

Events can be private with an invite list (e.g., birthday dinner) or public with no invite list (e.g., concert), each having a page showing details, shareability, and RSVPs in four buckets (going/maybe/not_going/not_responded) where stated intent may not match actual attendance. Event pages also support comments, likes, photo posts, and shares, which can appear in the news feed and be interacted with via permalinks.