C.O.R.E., Yahoo's content optimization and relevance engine, leverages user data to fuel a set of algorithms aimed at delivering more personally relevant content. C.O.R.E. tests content's popularity by displaying it to a small user group, and then displays the most popular items to the majority of users. Every 5 minutes, the system processes 100 GB of user feedback and updates its algorithm to direct stories to the right users. C.O.R.E. can optimize for multiple objectives, such as revenue, user engagement, and personalization. It has resulted in a 270% improvement in click rates at Yahoo and contributed to a billion clicks on Yahoo's home page in both January and March.