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Meta·Data Scientist·Technical Phone Screen·Senior

Senior
Jul 2026

Summary

Meta DS interview on the ads side. One meaty experiment design question that covered a lot of ground, from traffic splits to stakeholder communication. Felt like a case study more than a typical stats quiz.

Questions Asked (1)

Q1

You've trained a new ad recommendation model and want to know if it should replace the current one. Walk through how you'd design the experiment, what metrics you'd track, how you'd frame results differently for a finance exec versus a growth exec, and what your launch or rollback decision framework looks like.

A/B Testing & ExperimentationProduct Analytics & MetricsStakeholder Management
Author's notes

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Suggested Approach

Structure your answer around a controlled A/B test with a clear hypothesis, primary and guardrail metrics, and a decision framework that balances statistical significance with business impact. Emphasize tailoring communication to each stakeholder's priorities: finance cares about ROI and cost efficiency, while growth cares about user engagement and long-term value. Conclude with a launch/rollback framework that includes pre-defined thresholds and a plan for monitoring post-launch.

Pro tip: Propose a holdback group to measure long-term effects and avoid confounding from seasonality or novelty effects. Also, mention that you'd align on success criteria with stakeholders before the test to prevent post-hoc debates.

1. Define Hypothesis and Success Metrics

Clearly state the hypothesis (e.g., new model increases CTR without hurting user experience) and select primary metrics (e.g., CTR, conversion rate) and guardrail metrics (e.g., user satisfaction, latency, revenue per user).

2. Design the Experiment

Choose a randomized controlled trial with proper power analysis, determine sample size and duration, and ensure randomization unit (e.g., user-level) and traffic split are appropriate. Consider holdback for long-term measurement.

3. Analyze Results and Validate

Check for statistical significance, practical significance, and novelty effects. Segment results by user cohorts to understand heterogeneous treatment effects and ensure guardrails are not violated.

4. Tailor Communication to Stakeholders

For finance execs, frame results in terms of incremental revenue, ROI, and cost savings; for growth execs, focus on user engagement, retention, and long-term growth metrics. Use clear, non-technical language and visualizations.

5. Launch or Rollback Decision Framework

Pre-define thresholds for success (e.g., primary metric lift > X% with no guardrail degradation). If met, launch with gradual rollout and monitoring; if not, rollback or iterate. Include a plan for post-launch monitoring and alerting.

Key Points to Mention

  • Randomized controlled trial (A/B test) with proper power analysis and sample size calculation
  • Primary metric (e.g., CTR) and guardrail metrics (e.g., user satisfaction, latency, revenue)
  • Statistical significance vs. practical significance, and novelty effects
  • Segmentation analysis to understand heterogeneous treatment effects
  • Stakeholder-specific framing: finance (ROI, cost) vs. growth (engagement, retention)
  • Pre-defined launch/rollback criteria and post-launch monitoring plan

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