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Meta·Data Scientist·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

Meta DS interview focused on product analytics for Oculus. One SQL question with a conceptual follow-up about metric definitions. Pretty straightforward but the open-ended 'which metric is best' part is where I think they actually care about your answer.

Questions Asked (2)

Q1

Write a SQL query to find the most-used app over the last 7 days relative to a given date. Return the app ID, app name, and your chosen usage metric.

Product Analytics & MetricsData Modeling
Author's notes

I went with session count as my metric since it felt cleaner to defend than total duration.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the usage metric (e.g., daily active users, sessions, or time spent) and the definition of 'most-used' (e.g., highest average DAU over the 7 days). Then, write a SQL query that aggregates usage per app per day, filters to the 7-day window relative to the given date, computes the chosen metric, and returns the top app.

Pro tip: Always state your assumptions about the metric and time window explicitly, and consider edge cases like apps with missing data on some days. Mention that you would validate the metric with product stakeholders to ensure it aligns with business goals.

1. Clarify the metric and definitions

Define what 'most-used' means (e.g., highest average daily active users, total sessions, or total time spent) and confirm the 7-day window (e.g., the 7 days ending on the given date).

2. Identify tables and columns

Assume a usage table with columns like app_id, user_id, date, and possibly session_count or duration. Also assume an apps table with app_id and app_name.

3. Aggregate usage per app per day

Write a subquery or CTE that groups by app_id and date, computing the daily metric (e.g., COUNT(DISTINCT user_id) for DAU).

4. Compute the 7-day metric and rank

Filter to the 7-day window, then aggregate across days (e.g., AVG(daily_metric)) and order descending to find the top app.

5. Join with app metadata and return result

Join the aggregated result with the apps table to get app_name, and select the top app (e.g., using LIMIT 1 or a window function).

Key Points to Mention

  • Choice of usage metric (DAU, sessions, time spent) and rationale
  • Handling of missing dates or apps with zero usage
  • Use of window functions or subqueries for ranking
  • Assumption about the given date and time zone
  • Potential need to deduplicate user activity
  • Scalability considerations for large datasets

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

Q2

What are the trade-offs between different definitions of 'most used app': number of sessions, total time spent, and unique users?

Product Analytics & MetricsTechnical Trade-offs
Author's notes

Session count rewards apps people open frequently but briefly, like a news app.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the business objective behind 'most used app' and the decision it will inform, then systematically compare the three definitions across dimensions like user intent, engagement quality, and business impact. Conclude by recommending a definition or composite metric based on the specific context and trade-offs.

Pro tip: Acknowledge that no single metric is perfect and propose a composite or tiered approach (e.g., primary metric with guardrails) to show strategic thinking. Also, mention that the choice should align with the company's north star and be validated through A/B testing or causal analysis.

1. Clarify the objective

Ask what decision the 'most used app' metric will inform (e.g., resource allocation, feature prioritization) and who the stakeholders are. This ensures the definition aligns with business goals.

2. Define each metric

Clearly define number of sessions, total time spent, and unique users, including how they are measured (e.g., session timeout, active vs. passive time).

3. Analyze trade-offs

Compare the metrics on dimensions such as sensitivity to outliers, ability to capture depth vs. breadth of engagement, susceptibility to gaming, and alignment with user value.

4. Consider context and edge cases

Discuss how the choice might vary by app type (e.g., utility vs. social) and user segments, and potential pitfalls like double-counting or bot traffic.

5. Recommend and validate

Propose a primary metric or composite, suggest guardrail metrics, and outline how to validate the choice (e.g., correlation with retention, A/B testing).

Key Points to Mention

  • Number of sessions: captures frequency but may overvalue brief, low-value interactions; sensitive to session definition.
  • Total time spent: reflects depth of engagement but can be skewed by passive usage (e.g., background audio) and may not indicate active use.
  • Unique users: measures reach but not frequency or depth; may be inflated by one-time users and not reflect habitual usage.
  • Trade-offs: frequency vs. depth vs. breadth; susceptibility to gaming; alignment with business goals like ad revenue or user retention.
  • Composite metrics: combining metrics (e.g., DAU/MAU ratio, sessions per user, time per session) can provide a more balanced view.
  • Contextual factors: app category, user intent, and platform (mobile vs. desktop) influence which metric is most appropriate.

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