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Affirm·Data Scientist·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Affirm data scientist interview with a fraud risk scenario question. Pretty technical, focused on how you'd actually debug a real production issue rather than anything theoretical.

Questions Asked (1)

Q1

Credit card approval rates have been stable for months and then suddenly drop in a single day. Walk through how you'd diagnose what happened, what data you'd pull, and what your leading hypotheses would be.

Root Cause AnalysisProduct Analytics & MetricsA/B Testing & Experimentation
Author's notes

This one took me a second to get organized.

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AI HintsAI Generated

Suggested Approach

Start by confirming the drop is real and not a data pipeline or reporting artifact, then segment the metric by key dimensions (e.g., time, product, user cohort, geography, device) to localize the change. Form hypotheses around internal changes (e.g., model updates, policy changes, bugs) and external factors (e.g., competitor actions, economic events), and validate with data pulls and if possible, a quick experiment or backtest.

Pro tip: Always check data quality first—many 'sudden drops' are due to logging errors, ETL failures, or dashboard bugs. Also, consider seasonality and day-of-week effects; a single-day drop might be a holiday or payday anomaly.

1. Validate the metric and data pipeline

Verify the drop is real by checking data freshness, completeness, and consistency across sources. Ensure no ETL issues, logging errors, or dashboard glitches.

2. Segment and localize the drop

Break down approval rates by dimensions like time (hourly), product type, user demographics, geography, device, and acquisition channel to identify where the drop is concentrated.

3. Form and prioritize hypotheses

List potential internal causes (e.g., model deployment, policy change, bug) and external causes (e.g., competitor promo, economic news, seasonality). Prioritize based on likelihood and impact.

4. Pull relevant data and test hypotheses

Query additional data (e.g., model scores, rule triggers, user behavior, external events) to confirm or refute each hypothesis. Use statistical tests or backtests if applicable.

5. Synthesize findings and recommend actions

Summarize the root cause, quantify impact, and suggest immediate fixes or further monitoring. If cause is external, consider adjustments to strategy.

Key Points to Mention

  • Check for data quality issues (e.g., missing data, pipeline failures) before assuming a real drop.
  • Segment by time (hourly), product, user cohort, geography, device, and acquisition channel to localize the issue.
  • Consider internal changes: model updates, underwriting policy changes, bug in approval logic, or system outages.
  • Consider external factors: competitor actions, economic events, seasonality, or day-of-week effects.
  • Pull data on model scores, rule triggers, and user behavior to test hypotheses.
  • Quantify impact and recommend immediate actions (e.g., rollback, fix bug) or further investigation.

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