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Coinbase·Data Scientist·Technical Phone Screen·Senior

Senior
Feb 2025Remote

Summary

Coinbase data science interview with a meaty causal inference question built around a Super Bowl ad scenario. One question, but it had about six sub-problems packed inside it. Not a casual screen.

Questions Asked (1)

Q1

CoinFactory ran a 60-second Super Bowl ad with a QR code on Feb 9, 2025. Walk through how you'd estimate the incremental sign-ups attributable to that ad in the first 48 hours, including your identification strategy, data sources, deduplication approach, a back-of-the-envelope calculation with specific numbers provided, and how you'd validate the final estimate.

A/B Testing & ExperimentationProduct Analytics & MetricsRoot Cause Analysis
Author's notes

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AI HintsAI Generated

Suggested Approach

Use a difference-in-differences design comparing sign-ups during the ad window to a synthetic control constructed from pre-ad periods and similar non-exposed markets, then adjust for QR code scans and deduplicate users across channels. Validate by triangulating with holdout tests, funnel analysis, and sensitivity checks on key assumptions.

Pro tip: Acknowledge that the Super Bowl creates a massive simultaneous shock, so a simple pre-post comparison is biased; instead, emphasize using a control group (e.g., regions with no ad exposure or historical baselines) and clearly state assumptions about parallel trends.

1. Define the counterfactual and identification strategy

Establish what sign-ups would have occurred without the ad by using a difference-in-differences approach with a control group (e.g., similar time periods in previous years or markets not exposed to the ad). Clearly state the parallel trends assumption and how you'd test it.

2. Identify data sources and deduplicate users

List internal data (sign-up timestamps, acquisition channel, device ID, QR scan events) and external data (Super Bowl viewership ratings, social media mentions). Deduplicate by matching user IDs, emails, or device fingerprints across channels to avoid double-counting.

3. Perform back-of-the-envelope calculation

Estimate incremental sign-ups using specific numbers: e.g., 100M viewers, 1% QR scan rate = 1M scans, 20% conversion to sign-up = 200K sign-ups. Adjust for baseline sign-ups (e.g., 50K in 48 hours without ad) to get incremental lift of 150K.

4. Validate the estimate with multiple methods

Cross-check with A/B testing if a holdout group exists, funnel analysis to see drop-off from scan to sign-up, and sensitivity analysis on assumptions (e.g., scan rate, conversion rate). Compare with external benchmarks and historical campaign performance.

5. Communicate uncertainty and limitations

Present a range (e.g., 120K–180K incremental sign-ups) rather than a point estimate, and discuss potential confounders like concurrent promotions, media coverage, and seasonality. Recommend further experiments to refine the estimate.

Key Points to Mention

  • Difference-in-differences or synthetic control to isolate causal impact
  • Deduplication across QR scans, app installs, and web sign-ups using user identifiers
  • Back-of-the-envelope calculation with explicit assumptions (viewership, scan rate, conversion rate)
  • Validation via holdout groups, funnel analysis, and sensitivity checks
  • Acknowledgment of confounders (e.g., organic buzz, other ads) and use of control markets
  • Communication of uncertainty with confidence intervals or ranges

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