Scenario

YouTube observes a sudden decline in daily active users (DAU) and total watch time across the platform.

Task

Design a systematic diagnosis plan for the drop in usage. Specify:

• Which engagement and funnel metrics you would inspect.
• How you would segment users to localize the issue.
• What further analyses or experiments you would run to confirm root causes.

Context and Assumptions

Assume you have access to event logs (impressions, clicks, plays, session starts/ends), QA/monitoring dashboards, experiment/feature rollout logs, content supply stats, and standard experimentation tools (A/B, holdouts, geo rollouts/rollbacks).

Notes

• Frame the analysis using the acquisition → activation → engagement → retention funnel.
• Segment by device/OS/app-version, geography/time zone, traffic source, and recent feature/model launches.
• Compare pre- and post-drop cohorts, and consider hold-out or rollback tests to isolate factors.