##### Scenario Online experimentation and causal analysis for a consumer app. ##### Question An A/B test changed a call-to-action button from green (control) to red (treatment) and retention dropped. Describe the diagnostics you would run to decide whether uneven traffic allocation or other experiment-quality issues drove the result. You are asked to measure the causal impact of receiving negative reviews on a merchant’s coupon repurchase rate. Outline the data you need and the methodology you would use to obtain an unbiased estimate. ##### Hints Think about sample-ratio mismatch checks, covariate balance, time windows, difference-in-differences, matching/propensity scores, or holdout experiments.