Choose Randomization Unit and Mitigate Network Effects

Quick Overview

This interview question evaluates statistical assumptions, formulas, estimation strategy, uncertainty, edge cases, and interpretation in a realistic interview setting. A strong answer for Choose Randomization Unit and Mitigate Network Effects states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Choose Randomization Unit and Mitigate Network Effects

Company: Meta

Role: Data Scientist

Category: Statistics & Math

Difficulty: hard

Interview Round: Onsite

##### Scenario A/B test for new Messenger feature with possible network effects ##### Question Describe how you would choose the randomization unit for this experiment, justify it, and detail statistical methods to detect and mitigate network effects if present. ##### Hints Discuss user-level vs cluster-level, interference assumption, CUPED or diff-in-diff.

Quick Answer: This interview question evaluates statistical assumptions, formulas, estimation strategy, uncertainty, edge cases, and interpretation in a realistic interview setting. A strong answer for Choose Randomization Unit and Mitigate Network Effects states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

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Aug 4, 2025, 10:55 AM
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Choose Randomization Unit and Mitigate Network Effects

A/B Test Design for a New Messenger Feature with Network Effects

Context

You are designing an A/B test for a new Messenger feature in a social messaging app. Users communicate via one-to-one and group conversations. Because people interact, there is a risk that a participant's assignment could influence their peers' outcomes (network interference), violating the standard "no interference" assumption of A/B tests.

Tasks

  1. Choose an appropriate randomization unit (e.g., user-level, conversation/thread-level, cluster/graph-level) and justify your choice given potential network effects.
  2. Describe practical diagnostics and statistical tests you would use to detect network effects if they occur.
  3. Propose design and analysis methods to mitigate bias from network effects and to estimate both direct and spillover effects. Where useful, mention methods such as CUPED and difference-in-differences.

Clarifying Questions to Ask Guidance

  • Clarify the random variables, distributional assumptions, independence assumptions, and desired output.
  • Show enough derivation for the interviewer to follow the reasoning.
  • Explain how you would validate the result with simulation or sensitivity checks.

What a Strong Answer Covers Guidance

  • A correct setup with definitions, formulas, and boundary conditions.
  • A step-by-step derivation or estimation plan.
  • Interpretation of the result, including uncertainty and practical limitations.
  • Checks for assumptions, edge cases, and numerical stability.

Follow-up Questions Guidance

  • How would the result change if the assumptions were relaxed?
  • Can you verify the answer with a simulation?
  • What is the most likely source of estimation error?
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