Investigate Yahoo Mail's 10% DAU Decline Causes

Q: Investigate Yahoo Mail's 10% DAU Decline Causes

This is a Analytics & Experimentation interview question from Yahoo for Data Scientist roles. View the full question and solution on PracHub.

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Question

Investigate a 10% DAU Drop in Yahoo Mail

Scenario

Yahoo Mail suddenly reports a 10% decline in daily active users (DAU).

Task

Walk through how you would investigate and diagnose the root cause of this 10% DAU drop. Specify:

What data you would pull.
Which funnels or cohorts you would examine.
How you would rule out internal versus external factors.

Hints

Form a hypothesis tree.
Segment traffic by platform (web, iOS, Android), geography, and user cohorts (new vs. returning, tenure).
Inspect release logs, outages/incidents, A/B experiments, feature flags.
Check marketing changes, seasonality/day-of-week/holidays, and competitor or ecosystem news.

Minimal context/assumptions

DAU = count of unique accounts with at least one qualifying session or key event (e.g., inbox_view, email_read, compose_send) in a calendar day.
Yahoo Mail traffic spans web and mobile apps; notifications/push and email delivery ecosystem can affect engagement.