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TikTok·Data Scientist·Technical Phone Screen·Senior

Senior
May 2026

Summary

TikTok DS interview that was basically a single sprawling case study on paywall experimentation. Dense question, lots of sub-parts, felt more like a take-home prompt squeezed into a live session.

Questions Asked (1)

Q1

You're launching a new paywall where users are likely to share links with non-paying users. How do you define success metrics and design an experimentation strategy that accounts for interference, variance reduction, power calculations, sequential monitoring, and the final rollout decision?

A/B Testing & ExperimentationPricing & MonetizationProduct Analytics & Metrics
Author's notes

This was a lot.

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AI HintsAI Generated

Suggested Approach

Start by defining success metrics that capture both direct revenue and network effects, then outline an experimentation strategy that addresses interference through cluster randomization or other designs. Incorporate variance reduction, power calculations, sequential monitoring, and a decision framework for rollout.

Pro tip: Proactively discuss the trade-off between cluster randomization and individual randomization, and propose a method to measure and adjust for interference, such as using a exposure-based analysis or a causal inference technique.

1. Define Success Metrics

Identify primary metrics (e.g., revenue per user, conversion rate) and guardrail metrics (e.g., user engagement, churn). Consider network effects by including metrics like virality or sharing rate.

2. Design Experiment to Handle Interference

Choose a randomization unit (e.g., user, cluster) that minimizes interference. Consider cluster randomization (e.g., by geography or social graph clusters) or switchback designs. Plan to measure interference and adjust analysis.

3. Apply Variance Reduction and Power Analysis

Use techniques like CUPED or stratification to reduce variance. Conduct power calculations accounting for cluster randomization and interference, ensuring adequate sample size.

4. Implement Sequential Monitoring

Set up sequential testing with alpha spending or group sequential boundaries to allow early stopping for efficacy or futility while controlling Type I error.

5. Make Rollout Decision

Define decision criteria based on statistical significance, practical significance, and guardrail metrics. Consider a phased rollout to monitor long-term effects and interference.

Key Points to Mention

  • Interference and network effects in paywall experiments
  • Cluster randomization or other designs to mitigate interference
  • Variance reduction techniques like CUPED
  • Power calculations accounting for clustering
  • Sequential monitoring with alpha spending
  • Decision framework for rollout including guardrail metrics

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