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Snapchat·Data Scientist·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Snapchat data scientist interview focused on two product decision cases: banner ads and a group-story feature. Both questions pushed into experiment design territory pretty fast, which I wasn't fully ready for.

Questions Asked (2)

Q1

What metrics would you track to measure the impact of adding a banner ad, and how would you design and analyze an A/B test to decide on launch, including how you'd handle accidental clicks?

A/B Testing & ExperimentationProduct Analytics & MetricsPricing & Monetization
Author's notes

The accidental clicks part is what tripped me up.

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AI HintsAI Generated

Suggested Approach

Start by defining a metric framework that covers ad revenue, user engagement, and user experience, then outline a rigorous A/B test design with randomization, sample size, and guardrail metrics. Finally, address accidental clicks by proposing methods to detect and mitigate them, and explain how to analyze their impact on the decision.

Pro tip: Emphasize that accidental clicks can inflate CTR and mislead launch decisions; propose using dwell time or post-click behavior to filter them out, and consider running a holdout group to measure long-term effects.

1. Define Success Metrics

Identify primary metrics (e.g., ad revenue per user, CTR) and secondary metrics (e.g., DAU, session length, retention) to capture both monetization and user experience impacts.

2. Design the A/B Test

Randomize users into control (no banner) and treatment (banner) groups, determine sample size and duration based on power analysis, and pre-register hypotheses and metrics.

3. Address Accidental Clicks

Define accidental clicks (e.g., clicks with very short dwell time or immediate back navigation) and plan to measure them via event logging; consider excluding them from primary analysis or analyzing separately.

4. Analyze Results and Make Decision

Compare metrics between groups using statistical tests, check guardrail metrics for negative impacts, and decide launch based on net positive effect and business goals.

Key Points to Mention

  • Metric framework: revenue (eCPM, ARPU), engagement (CTR, dwell time), user experience (retention, DAU, session frequency)
  • A/B test design: randomization unit (user-level), control/treatment setup, power analysis for sample size, test duration
  • Accidental clicks: define via dwell time threshold or bounce rate, measure with event tracking, analyze impact on CTR and revenue
  • Guardrail metrics: ensure no harm to core user behaviors (e.g., snaps sent, stories viewed)
  • Statistical analysis: use t-tests or bootstrapping for significance, check for novelty effects, segment by user demographics
  • Decision criteria: launch if primary metric improves without hurting guardrails, consider long-term holdout for retention impact

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

Q2

For a new group-story feature, what success metrics would you define and how would you set up the experiment, including choice of randomization unit, sample size, and how long to run it?

A/B Testing & ExperimentationProduct Sense & IdeationProduct Analytics & Metrics
Author's notes

This one felt more comfortable.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the feature's goal (e.g., increase group engagement and content creation) and then define a metric hierarchy: primary success metric, secondary metrics, and guardrail metrics. For the experiment, specify the randomization unit (e.g., user or group), calculate sample size based on desired power and minimum detectable effect, and determine run duration considering novelty effects and business cycles. Finally, discuss analysis plan including heterogeneous treatment effects and potential pitfalls.

Pro tip: Emphasize that the randomization unit should align with the metric's unit of analysis to avoid dilution or contamination; for group-story features, randomizing by group may be more appropriate than by user, but consider network effects. Also, mention that you would run an A/A test or check pre-experiment balance to validate the setup.

1. Clarify feature and goals

Ask clarifying questions to understand what the group-story feature entails (e.g., collaborative stories within friend groups) and what business objectives it serves (e.g., increase daily active users, time spent, or content creation).

2. Define success metrics

Propose a primary metric (e.g., number of group stories created per user per week) and secondary metrics (e.g., group story views, reactions, retention). Include guardrail metrics (e.g., app performance, user reports) to ensure no negative impact.

3. Design experiment

Choose randomization unit (e.g., user or group) based on where the treatment is applied and how metrics are measured. Discuss potential interference and consider cluster randomization if needed.

4. Determine sample size and duration

Calculate required sample size using power analysis (e.g., 80% power, 5% significance, minimum detectable effect from historical data or business relevance). Estimate run time based on traffic and desired sample size, accounting for novelty and primacy effects.

5. Analysis and decision

Outline analysis plan: compare primary metric between control and treatment, check guardrails, segment by user demographics or group size, and decide whether to launch, iterate, or abandon based on results.

Key Points to Mention

  • Metric hierarchy: primary, secondary, guardrail metrics with clear definitions and units of analysis.
  • Randomization unit: user-level vs. group-level, considering network effects and interference.
  • Sample size calculation: power, significance level, MDE, and variance estimation.
  • Experiment duration: account for novelty effects, weekly seasonality, and sufficient time to observe long-term behavior.
  • Analysis plan: intention-to-treat, heterogeneity, and multiple testing corrections.
  • Potential pitfalls: dilution, contamination, and Simpson's paradox.

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