Diagnose 10–11% usage drop across geos

US usage is down 10% and Mexico is down 11%. List plausible confounders (seasonality, pricing, outages, marketing mix, competitor moves, feature rollouts, macro). Propose an experiment to isolate causality: define the unit of randomization (user or geo), exposure and segmentation, primary metric and guardrails, duration and power, and pre-registration. If an experiment is infeasible, outline a difference-in-differences or synthetic control with explicit identification assumptions and diagnostics. Specify which covariates to stratify or control for, how you would slice results, and how you would present findings and confidence intervals to stakeholders along with remediation options.