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This is a medium difficulty Analytics & Experimentation question, commonly asked during Technical Screen rounds at Yahoo.

What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Yahoo during technical interviews.

Investigate Yahoo Mail's 10% DAU Decline Causes

Last updated: Mar 29, 2026

Quick Overview

This question evaluates competency in product analytics, causal reasoning, and diagnostic investigation of user engagement metrics for an email service experiencing a 10% DAU decline.

Yahoo

Jul 12, 2025, 6:59 PM

Data Scientist

Technical Screen

Analytics & Experimentation

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.

Solution

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