Evaluate an email test with confounding

A marketing team wants to evaluate a new email campaign. They tested **Email A** and **Email B** across **two cities (San Francisco and New York)** over **two weeks**. The raw results appear contradictory: - Within each city or week, **Email B** seems to outperform **Email A**. - But when all observations are combined, **Email A** appears better overall. How would you determine which email is actually better? Explain how **Simpson's paradox** could arise here, what metrics you would inspect, what confounding factors might exist, whether you can compute a **confidence interval**, and how you would redesign or rerun the experiment if needed.