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Meta·Data Scientist·Technical Phone Screen·Senior

Senior
May 2026

Summary

Meta DS interview with a meaty A/B testing case about rolling out a new payment method. The tricky part wasn't designing the experiment, it was handling the conflicting metrics at the end.

Questions Asked (1)

Q1

Design an A/B experiment to evaluate whether a new payment method should be launched nationwide. If conversion rate goes up but average order value drops, how do you reconcile those two signals and present a recommendation to the product team?

A/B Testing & ExperimentationProduct Analytics & MetricsCross-functional Alignment
Author's notes

The experiment design part I felt okay about.

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AI HintsAI Generated

Suggested Approach

Start by outlining a rigorous A/B test design with clear hypotheses, primary and guardrail metrics, and power analysis. Then, when addressing the conflicting signals, emphasize that conversion rate and AOV must be evaluated together using a north-star metric like revenue per user, and consider segment-level impacts and long-term effects. Finally, recommend a decision framework that weighs statistical significance, practical significance, and business strategy, and propose next steps such as deeper analysis or a follow-up experiment.

Pro tip: Always tie the metrics back to the company's overarching goal (e.g., total revenue or profit) and show that you understand trade-offs; product teams appreciate a clear recommendation with quantified risks rather than just data.

1. Define the experiment and metrics

Clearly state the hypothesis, primary metric (e.g., conversion rate), secondary metrics (e.g., AOV), and guardrail metrics (e.g., revenue per user, customer satisfaction). Include sample size and duration calculations.

2. Analyze the results holistically

Examine both conversion rate and AOV, and compute a combined metric like revenue per user. Check for statistical significance and confidence intervals for each metric.

3. Investigate segment-level and long-term effects

Break down results by user segments (e.g., new vs. existing, geography, device) to see if the drop in AOV is concentrated in certain groups. Consider long-term value and repeat purchase behavior.

4. Weigh trade-offs and business impact

Assess whether the increase in conversion compensates for the decrease in AOV in terms of total revenue or profit. Consider strategic factors like market competitiveness and user acquisition.

5. Formulate a recommendation and next steps

Provide a clear recommendation (launch, not launch, or iterate) backed by data, and suggest follow-up actions such as a longer-term holdout or a modified experiment to optimize the payment method.

Key Points to Mention

  • Use of a north-star metric like revenue per user to reconcile conflicting signals
  • Statistical significance and confidence intervals for both metrics
  • Segment analysis to identify heterogeneous treatment effects
  • Consideration of long-term effects and novelty bias
  • Business context and strategic alignment (e.g., market expansion vs. profitability)
  • Proposal for follow-up experiments or deeper analysis if results are ambiguous

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