Define and measure project metrics: For a project of your choice, specify primary outcome metrics, secondary metrics, and guardrails. Precisely define each metric (events, windows, denominators), outline an instrumentation and data-quality plan, and design an experiment or observational evaluation covering sampling, statistical power, expected effect size, seasonality, and heterogeneity. Discuss pitfalls such as metric gaming, selection bias, and Simpson's paradox, and explain how you would monitor and alert on regressions.