Your question is Measuring Design Success. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Explain how you determine which metrics to use and how you collected them to evaluate a design. Describe how you would connect design goals to measurable outcomes, select primary and guardrail metrics, and combine quantitative and qualitative evidence. Explain how you would ensure the data is reliable and use it to make a design decision.