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Meta·Data Scientist·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Meta DS interview with a meaty experiment analysis question. The whole thing revolved around one scenario but it had a lot of layers to unpack, more than I expected from a single prompt.

Questions Asked (1)

Q1

An ad-ranking algorithm shows a 5% overall CTR lift but a 100% lift specifically for Indian males aged 18-24. What could explain that gap, how would you confirm the lift is real and not noise, and what else would you look at before a global rollout?

A/B Testing & ExperimentationProduct Analytics & MetricsRoot Cause Analysis
Author's notes

This is the kind of question where you think you're doing well and then realize halfway through you forgot to mention Simpson's paradox.

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AI HintsAI Generated

Suggested Approach

Start by acknowledging the overall lift, then systematically explore potential causes for the segment-specific gap, such as data quality, novelty effects, or algorithmic bias. Next, outline a rigorous validation plan using statistical tests and robustness checks. Finally, discuss broader considerations like long-term effects, fairness, and global generalizability before recommending a rollout.

Pro tip: Always question whether the segment lift is due to a real behavioral change or an artifact like Simpson's paradox; check if the segment's baseline CTR is unusually low, making the lift appear dramatic. Also, consider that a 100% lift in a small segment might not be statistically significant if the sample size is small.

1. Investigate potential explanations for the gap

Examine data quality, segment size, novelty effects, and algorithmic factors that could cause a disproportionate lift in one segment. Consider Simpson's paradox where the overall lift masks segment-level variations.

2. Validate the lift statistically

Check statistical significance of the segment lift using appropriate tests (e.g., t-test, bootstrap) and ensure adequate power. Look for p-hacking or multiple comparisons issues, and verify with holdout data.

3. Assess robustness and generalizability

Test if the lift persists over time (not just novelty), across similar segments, and in different geographies. Consider potential biases like selection bias or confounding variables.

4. Evaluate broader business and ethical implications

Consider long-term metrics (retention, user satisfaction), fairness across demographics, and potential backlash. Check if the algorithm optimizes for short-term CTR at the expense of other goals.

5. Recommend next steps for rollout

Propose a phased rollout with continued monitoring, A/B tests in other regions, and guardrail metrics to detect unintended consequences.

Key Points to Mention

  • Simpson's paradox and segment-level analysis
  • Statistical significance, power, and multiple comparisons correction
  • Novelty effect and long-term metric tracking
  • Data quality issues (e.g., logging errors, bot traffic)
  • Algorithmic bias and fairness considerations
  • Global rollout strategy with phased testing and guardrail metrics

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