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Design experiments under network interference

Last updated: Mar 29, 2026

Quick Overview

This question evaluates a data scientist's competence in experimental design and causal inference under network interference, assessing understanding of clustering strategies, exposure and exclusion definitions, contamination control, design effect and sample-size implications, estimation of intra-cluster correlation, and mixed-effects analysis for evolving clusters. Commonly asked in Analytics & Experimentation interviews to probe the ability to preserve internal validity while managing operational feasibility in two-sided marketplaces, it tests both conceptual understanding of interference and practical application skills in design and analysis planning.

  • hard
  • Meta
  • Analytics & Experimentation
  • Data Scientist

Design experiments under network interference

Company: Meta

Role: Data Scientist

Category: Analytics & Experimentation

Difficulty: hard

Interview Round: Onsite

Design an A/B test for a search‑ranking change in a 2‑sided marketplace with cross‑seller spillovers and consumer social contagion. Choose between cluster randomization (e.g., by seller or geography) and ego‑cluster randomization; precisely define exposure and exclusion criteria. Given mean cluster size m=50 and intra‑cluster correlation ρ=0.02, compute the design effect and the required sample‑size inflation versus individual randomization; explain how you would estimate ρ pre‑experiment from historical data. How will you prevent treatment contamination during reassignment and validate success using invariant metrics and SSRM under clustering? If clusters evolve over time, propose a rehashing schedule and an analysis plan using mixed‑effects models with cluster random intercepts.

Quick Answer: This question evaluates a data scientist's competence in experimental design and causal inference under network interference, assessing understanding of clustering strategies, exposure and exclusion definitions, contamination control, design effect and sample-size implications, estimation of intra-cluster correlation, and mixed-effects analysis for evolving clusters. Commonly asked in Analytics & Experimentation interviews to probe the ability to preserve internal validity while managing operational feasibility in two-sided marketplaces, it tests both conceptual understanding of interference and practical application skills in design and analysis planning.

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Meta
Oct 13, 2025, 9:49 PM
Data Scientist
Onsite
Analytics & Experimentation
1
0

A/B Test Design for Search-Ranking in a Two-Sided Marketplace with Interference

Context

You need to evaluate a change to the search-ranking algorithm in a two-sided marketplace where:

  • Sellers can affect each other (cross-seller spillovers, e.g., inventory or ranking shifts that alter other sellers' exposure).
  • Consumers can influence each other (social contagion, e.g., shares, word-of-mouth).

Design an interference-aware experiment that preserves internal validity while remaining operationally feasible.

Tasks

  1. Choose a randomization strategy: cluster randomization (e.g., by seller or geography) vs. ego-cluster randomization. Justify the choice given cross-seller spillovers and consumer social contagion.
  2. Precisely define exposure and exclusion criteria to control interference.
  3. Compute design effect and sample-size inflation for clustering with mean cluster size m = 50 and intra-cluster correlation ρ = 0.02.
  4. Explain how to estimate ρ pre-experiment from historical data.
  5. Describe how to prevent treatment contamination during reassignment and how to validate success using invariant metrics and sample-size ratio mismatch (SSRM) under clustering.
  6. If clusters evolve over time, propose a rehashing (re-clustering) schedule and an analysis plan using mixed-effects models with cluster random intercepts.

Solution

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