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Meta·Data Scientist·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Meta DS interview with a meaty content moderation question that covered both offline model evaluation and online experimentation design. Pretty technical for a single question but that's Meta for you.

Questions Asked (1)

Q1

You have a machine learning model that flags harmful content for removal or down-ranking. Walk through how you'd evaluate it offline using a labeled validation set, then design an online experiment to test it in production, including hypotheses, variants, success metrics, and guardrails.

A/B Testing & ExperimentationProduct Analytics & MetricsTechnical Trade-offs
Author's notes

This is basically two questions stitched together and I didn't pace myself well.

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AI HintsAI Generated

Suggested Approach

Start by outlining offline evaluation using a labeled validation set, focusing on precision/recall trade-offs and threshold selection. Then design an online A/B test with clear hypotheses, variants, success metrics, and guardrails to measure real-world impact. Emphasize the importance of aligning offline metrics with online outcomes and iterating based on results.

Pro tip: Highlight the need to consider both user experience and fairness/bias implications, and propose a multi-metric evaluation framework that balances harm reduction with false positives. Show awareness of Meta's scale by discussing how to handle large-scale data and potential feedback loops.

1. Offline Evaluation Setup

Use a labeled validation set to compute precision, recall, F1, and AUC. Analyze performance across different content types and user segments to identify biases.

2. Threshold Selection and Trade-offs

Choose an operating threshold based on the desired balance between false positives (over-removal) and false negatives (harmful content left up). Consider business and ethical implications.

3. Online Experiment Design

Define a hypothesis (e.g., new model reduces harmful content prevalence without increasing false positives). Randomize users into control (current model) and treatment (new model) groups.

4. Success Metrics and Guardrails

Primary metrics: prevalence of harmful content, user reports, and engagement. Guardrails: false positive rate, user satisfaction, and fairness metrics across demographics.

5. Analysis and Iteration

Analyze results for statistical significance and practical impact. If successful, consider gradual rollout; if not, diagnose issues and iterate on model or threshold.

Key Points to Mention

  • Precision-recall trade-off and threshold tuning
  • Stratified evaluation by content type and user demographics
  • A/B test randomization unit (user-level vs. content-level)
  • Primary and guardrail metrics with clear definitions
  • Statistical power and sample size calculation
  • Potential feedback loops and long-term effects

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