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Meta·Software Engineer·Technical Phone Screen·Senior

Senior
May 2026

Summary

Meta data science interview with a classic experimentation design question. Pretty focused, just the one problem but they pushed hard on the details.

Questions Asked (1)

Q1

You're designing an A/B test to measure the effect of showing users content from people they don't follow in their feed. Walk through how you'd set this up with proper randomization.

A/B Testing & ExperimentationProduct Analytics & Metrics
Author's notes

This sounds clean on the surface but the randomization piece is where it gets tricky.

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AI HintsAI Generated

Suggested Approach

Start by defining the hypothesis and success metrics, then explain the randomization unit (e.g., user-level) and how to ensure proper assignment. Walk through the experiment setup, including control/treatment groups, guardrail metrics, and analysis plan, while addressing potential pitfalls like network effects and novelty effects.

Pro tip: At Meta, where social interactions are key, emphasize how you'd handle interference between users (e.g., if a user sees content from a non-followed person, that person's metrics might be affected). Mention techniques like cluster randomization or ego-network randomization to mitigate this.

1. Define Hypothesis and Metrics

Clearly state the hypothesis (e.g., showing non-followed content increases engagement) and select primary metrics (e.g., time spent, likes, comments) and guardrail metrics (e.g., user reports, unfollows).

2. Choose Randomization Unit and Assignment

Decide on the randomization unit (e.g., user-level) and explain how to randomly assign users to control (no non-followed content) and treatment (with non-followed content) groups, ensuring balanced groups.

3. Address Interference and Network Effects

Discuss potential interference (e.g., a user's behavior affecting others) and propose solutions like cluster randomization (randomizing by social clusters) or ego-network randomization.

4. Determine Sample Size and Duration

Calculate required sample size based on expected effect size, power, and significance level; set experiment duration to capture enough data and account for novelty effects.

5. Analyze Results and Validate

Plan for statistical analysis (e.g., t-test, regression), check for novelty/primacy effects, and validate that randomization worked (e.g., AA test, covariate balance).

Key Points to Mention

  • Randomization unit: user-level vs. session-level, and why user-level is typically preferred for social features.
  • Guardrail metrics: ensure user experience isn't harmed (e.g., increased reports, decreased satisfaction).
  • Network effects: how one user's treatment can affect control users, and mitigation strategies.
  • Novelty effect: initial spike in engagement may not persist; consider longer duration or holdout groups.
  • Statistical power: importance of pre-experiment power analysis to avoid false negatives.
  • AA test: run a test with no difference to validate randomization and metrics.

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