It's the responsibility of the Development Team to estimate the amount of work of Product Backlog
items and to select appropriate number of them for each Sprint. They also break down the items into
tasks during the Sprint.Measuring the project performance is the responsibility of the Product
Owner, while measuring the Sprint performance is done by the Development Team.Creating new Product
Backlog items, ordering them (prioritization) and making sure that everyone has a clear
understanding of them is the responsibility of the Product Owner.