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Google·Data Scientist·Technical Phone Screen·Senior

Senior
Jul 2026

Summary

Google DS interview with a product experimentation question centered on a real Maps UI change. Pretty clean setup but the depth expected was no joke.

Questions Asked (1)

Q1

The product team is considering moving the Google Maps search bar from the top of the screen to the bottom. Walk through how you would design an A/B test to evaluate this change, covering your hypothesis, primary and guardrail metrics, experiment unit, randomization strategy, sample size calculation, expected runtime, and how you'd interpret the results.

A/B Testing & ExperimentationProduct Analytics & MetricsProduct Sense & Ideation
Author's notes

This looks like a clean experiment question until you realize how many pieces they actually want you to hit.

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AI HintsAI Generated

Suggested Approach

Start by framing the change as a hypothesis about user behavior, then systematically design the A/B test covering all requested components. Emphasize the importance of guardrail metrics and practical considerations like network effects and sample size.

Pro tip: Mention that Google Maps has a global user base, so consider localization and device differences in your design. Also, highlight the need to monitor long-term effects and user satisfaction, not just short-term engagement.

1. Define Hypothesis and Metrics

State a clear hypothesis (e.g., moving the search bar to the bottom increases search engagement due to easier thumb access) and select primary metric (e.g., search queries per user) and guardrail metrics (e.g., app crashes, time to first search, user retention).

2. Choose Experiment Unit and Randomization

Decide on the randomization unit (e.g., user-level) and strategy (e.g., random assignment within each country/device type) to avoid contamination and ensure representative samples.

3. Calculate Sample Size and Runtime

Use power analysis to determine required sample size based on baseline metrics, minimum detectable effect, significance level, and power. Estimate runtime based on daily traffic and desired sample size.

4. Run Experiment and Monitor

Launch the experiment, monitor for technical issues and novelty effects, and ensure data quality. Consider running for at least one full week to capture weekly patterns.

5. Analyze and Interpret Results

Compare primary and guardrail metrics between control and treatment groups using statistical tests. Check for statistical significance, practical significance, and segment-level effects. Decide whether to launch, iterate, or abandon.

Key Points to Mention

  • Clear hypothesis with directional expectation
  • Primary metric tied to product goal (e.g., search engagement)
  • Guardrail metrics to ensure no negative impact (e.g., latency, crashes, retention)
  • Randomization unit (user-level) and strategy to avoid network effects
  • Sample size calculation using power analysis (alpha, beta, MDE)
  • Runtime estimation considering traffic and weekly seasonality
  • Interpretation: statistical significance, practical significance, and segment analysis

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.