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Meta·Data Scientist·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Meta DS interview with a stats-heavy scenario around feed ranking experiments. One question but it had enough layers to keep me busy for a while.

Questions Asked (1)

Q1

You have three feed-ranking experiments, all with negative engagement effects and known 95% confidence intervals: Treatment A at -5 (CI: -7.5 to -2.5), Treatment B at -15 (CI: -17 to -13), Treatment C at -12 (CI: -28 to -4). Interpret each interval and decide which, if any, you'd launch.

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

The twist is that all three are negative, so the instinct is to just say 'none of them' and move on.

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AI HintsAI Generated

Suggested Approach

Interpret each confidence interval in terms of statistical significance and practical impact, then weigh the trade-offs between effect size, uncertainty, and business risk. Conclude that none should be launched as-is, but recommend further investigation for treatments with promising signals or high uncertainty.

Pro tip: Emphasize that statistical significance alone isn't enough; consider the cost of a false negative (missing a good feature) versus a false positive (launching a harmful change), and align with product goals.

1. Interpret each confidence interval

For each treatment, determine whether the interval excludes zero (statistical significance) and describe the range of plausible effect sizes. Note that all intervals are entirely negative, indicating significant negative effects.

2. Assess practical significance and risk

Evaluate the magnitude of the effect and the width of the interval. A wider interval (e.g., Treatment C) indicates more uncertainty, which may warrant further data collection before making a decision.

3. Compare treatments and consider business context

Rank treatments by effect size and confidence. Treatment B has the most negative and precise estimate, making it the worst. Treatment A has the smallest negative effect, but still significant. Treatment C is highly uncertain.

4. Make a launch decision

Conclude that none should be launched because all show significant negative effects. However, if forced to choose, Treatment A is the least harmful, but it's still negative. Recommend not launching any and possibly investigating why all treatments hurt engagement.

5. Suggest next steps

Propose additional experiments or analyses to understand the negative effects, such as segment analysis, longer run time, or qualitative research. Consider whether the metric is appropriate or if there are novelty effects.

Key Points to Mention

  • Statistical significance: all intervals exclude zero, so all effects are significantly negative.
  • Practical significance: even the smallest effect (-5) may be unacceptable depending on the metric and business goals.
  • Uncertainty: Treatment C's wide interval suggests we need more data to estimate its true effect.
  • Trade-offs: launching a negative feature could harm user engagement and business metrics.
  • Decision criteria: typically, we require positive and significant effects to launch; here, none qualify.
  • Next steps: investigate root causes, run further experiments, or consider alternative designs.

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