Your work in Define and Measure has given you a clear mission for what you need to improve (Y metric), and you may even have some hunches about how to do this. In this part, we give you the guidance you need to formulate and test those hunches. Even better, we give you a methodical process for identifying, narrowing, testing, and validating exactly how you need to change your process to ensure it performs much better. In the Lean Six Sigma world, this means you’re moving through the Analyze and Improve phases of DMAIC. Then, after you’ve improved your process beyond the shadow of a doubt, you lock in your improvements during the Control phase.