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Meta·Data Scientist·Technical Phone Screen·Senior

Senior
May 2026

Summary

Data Scientist interview at Meta focused entirely on Stories as a product case. Four questions, all interconnected, building from basic evaluation metrics up to cross-app performance gaps. The experiment design question at the end was the toughest part.

Questions Asked (4)

Q1

How would you evaluate the performance of Instagram Stories as a feature?

Product Analytics & MetricsA/B Testing & Experimentation
Author's notes

Started with DAU lift and posting frequency, which felt safe.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the goal of evaluating Instagram Stories—whether it's to measure its success as a standalone feature or its impact on the broader Instagram ecosystem. Then, define a metric framework that covers engagement, retention, monetization, and network effects, and discuss how you would use A/B testing and causal inference to isolate the feature's impact.

Pro tip: Acknowledge that Instagram Stories is a mature feature, so focus on incremental improvements and trade-offs with other surfaces (e.g., Feed, Reels) rather than just basic engagement metrics. Show awareness of the competitive landscape (e.g., Snapchat) and how Stories contributes to Meta's overall mission.

1. Clarify the evaluation goal

Ask whether the goal is to assess Stories' overall health, its impact on Instagram's ecosystem, or a specific change. This determines the metrics and methods used.

2. Define success metrics

Identify key metrics across engagement (DAU, stories viewed/created, time spent), retention (stickiness, churn), monetization (ad revenue, conversion), and network effects (sharing, cross-posting).

3. Choose evaluation methods

Use A/B testing for causal impact of changes, holdout groups for long-term effects, and quasi-experimental designs when randomization isn't possible. Consider cohort analysis and user segmentation.

4. Analyze trade-offs and ecosystem impact

Examine how Stories affects other surfaces (e.g., Feed, Reels) and overall app usage. Look for cannibalization or synergy, and measure net impact on company goals.

5. Synthesize and recommend

Combine quantitative findings with qualitative insights (user feedback, market trends) to provide actionable recommendations for product improvements or strategic decisions.

Key Points to Mention

  • Define clear success metrics: engagement (views, creation, time spent), retention (DAU/MAU, churn), monetization (ad revenue, ARPU), and network effects (shares, cross-posting).
  • Use A/B testing and causal inference methods (e.g., difference-in-differences, propensity score matching) to measure impact, especially for mature features.
  • Consider long-term holdout groups to measure sustained effects and avoid novelty bias.
  • Segment users by demographics, geography, and behavior to uncover heterogeneous treatment effects.
  • Evaluate trade-offs with other Instagram surfaces (Feed, Reels, Explore) and overall app engagement.
  • Benchmark against competitors (e.g., Snapchat) and industry trends to contextualize performance.

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

Q2

What criteria would you use to decide whether to do a full launch after a pilot?

Product StrategyProduct Analytics & Metrics
Author's notes

Talked through pilot KPIs and how you'd benchmark against Snapchat.

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AI HintsAI Generated

Suggested Approach

Structure your answer around a decision framework that balances statistical rigor with business impact. Start by defining clear success metrics and guardrails from the pilot, then evaluate results against pre-set thresholds, and finally consider scalability and strategic alignment. Emphasize that the decision should be data-driven but also account for practical constraints and risks.

Pro tip: Show maturity by acknowledging that a pilot's results may not perfectly generalize due to novelty effects or limited scope, and propose a phased rollout with continued monitoring as a risk mitigation strategy.

1. Define success criteria upfront

Before the pilot, establish primary success metrics (e.g., conversion rate, engagement), guardrail metrics (e.g., latency, user satisfaction), and minimum detectable effect. This ensures objective evaluation.

2. Evaluate pilot results against criteria

Analyze pilot data to see if success metrics are met and guardrails are not violated. Use statistical tests to account for uncertainty and avoid false positives.

3. Assess scalability and generalizability

Consider whether the pilot's population, duration, and conditions are representative. Check for novelty effects, seasonality, or segment-specific performance that might not hold in full launch.

4. Estimate business impact and ROI

Quantify the expected impact of full launch on key business metrics (e.g., revenue, user growth) and compare against costs and potential risks.

5. Make a recommendation with risk mitigation

Decide whether to launch fully, iterate, or abandon. If launching, propose a phased rollout with monitoring to catch unforeseen issues.

Key Points to Mention

  • Statistical significance and confidence intervals
  • Guardrail metrics to ensure no harm
  • Novelty effect and long-term impact
  • Segment analysis (e.g., by demographics, geography)
  • Cost-benefit analysis and ROI
  • Phased rollout and A/B testing for validation

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

Q3

If Stories are cannibalising Feed posts, how do you respond to that?

Product Analytics & MetricsPricing & MonetizationRoot Cause Analysis
Author's notes

This one tripped me up more than I expected.

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AI HintsAI Generated

Suggested Approach

First, clarify what 'cannibalising' means in this context—whether it's a shift in user engagement from Feed to Stories or a net negative impact on overall platform metrics. Then, propose a structured analysis to determine if the cannibalisation is real, and if so, whether it's harmful or beneficial for the platform's goals. Finally, discuss potential responses based on data, such as product changes or metric adjustments.

Pro tip: Frame cannibalisation as a natural evolution of user behavior and focus on whether it drives overall engagement and revenue; often, internal cannibalisation is better than external competition. Show that you consider both short-term and long-term effects, and that you'd validate with experiments like holdouts.

1. Define and Validate the Cannibalisation

Clarify what metrics indicate cannibalisation (e.g., time spent, DAU, sessions) and check if the decline in Feed is offset by growth in Stories. Use data to confirm if it's a real trade-off or just correlation.

2. Assess Impact on Overall Goals

Evaluate whether the shift affects key platform objectives like total engagement, ad revenue, and user retention. Determine if the net effect is positive, negative, or neutral.

3. Identify Root Causes

Investigate why users are shifting: is it due to product changes, user preferences, or external factors? Segment users to see if the effect varies by demographics or behavior.

4. Propose Data-Driven Responses

Based on findings, suggest actions: if cannibalisation is harmful, consider product tweaks (e.g., cross-promotion, UI changes) or metric redefinition; if beneficial, double down on Stories.

5. Recommend Experimentation and Monitoring

Propose A/B tests or holdout groups to measure causal impact and set up ongoing monitoring to track the balance between Feed and Stories.

Key Points to Mention

  • Differentiate between cannibalisation and complementarity: Stories might increase overall engagement by attracting new users or increasing frequency.
  • Use metrics like total time spent, ad impressions, and revenue per user to evaluate net impact, not just Feed metrics.
  • Consider user segmentation: cannibalisation may be concentrated in certain demographics, requiring targeted strategies.
  • Highlight the importance of causal inference (e.g., experiments) to avoid misattributing trends.
  • Discuss trade-offs between short-term Feed engagement and long-term ecosystem health.
  • Mention potential product strategies like integrating Stories into Feed or optimizing ad load across formats.

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

Q4

Facebook Stories gets roughly half the views of Instagram Stories. Why might that be, and how would you design an experiment to investigate it?

A/B Testing & ExperimentationRoot Cause AnalysisProduct Sense & Ideation
Author's notes

Genuinely the hardest question of the session.

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AI HintsAI Generated

Suggested Approach

Start by hypothesizing possible reasons for the view gap, considering differences in user base, product design, and content ecosystems. Then propose a structured experiment to test the most impactful hypotheses, ensuring to define clear metrics and control for confounders. Finally, discuss how you would interpret results and iterate.

Pro tip: Acknowledge that correlation doesn't imply causation; many factors could contribute, so prioritize hypotheses based on potential impact and ease of testing. Also, consider that Facebook and Instagram have different user demographics and usage patterns, which might explain the gap without any product changes.

1. Clarify the metric and context

Define what 'views' means (e.g., a view counted after 3 seconds? total impressions?) and confirm the data source. Understand that Facebook and Instagram have different user bases, so a direct comparison might be misleading.

2. Generate hypotheses

Brainstorm possible reasons: differences in user demographics, interface placement, content type, social graph, or notification strategies. Group them into categories like product, user, and content.

3. Prioritize hypotheses

Assess which hypotheses are most plausible and testable. Consider impact on the metric and feasibility of experimentation. For example, UI placement might be easier to test than demographic shifts.

4. Design the experiment

Propose an A/B test where you manipulate one variable (e.g., move Stories to a more prominent location on Facebook) and measure the effect on views. Define control and treatment groups, sample size, duration, and success metrics.

5. Analyze and iterate

Outline how you would analyze results, check for statistical significance, and consider secondary metrics (e.g., engagement, retention). Discuss potential next steps based on findings.

Key Points to Mention

  • Differences in user demographics and behavior between Facebook and Instagram (e.g., age, frequency of use).
  • Product design factors: placement of Stories, entry points, and UI differences.
  • Content ecosystem: type of content shared, creators, and engagement patterns.
  • Network effects: how friends' usage influences one's own usage.
  • Experimental design: randomization, control groups, and avoiding confounders.
  • Metrics: define views clearly, and consider secondary metrics like time spent or retention.

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