Data Scientist interview questions and what they really test
Data interviews mix hands-on SQL and statistics with judgment questions about metrics and experiments. These are the patterns interviewers use to separate people who can query from people who can reason.
SQL & Data Modeling
What the interviewer is testing: writing/reasoning through a non-trivial query and schema trade-offs.
- Write a query to find the second-highest salary per department. Now handle ties.
- You have events and users tables. Compute 7-day retention by signup cohort. Walk the SQL.
- A dashboard query takes 40 seconds. Walk me through how you'd make it fast.
Statistics & Experimentation
What the interviewer is testing: A/B test design, significance, p-hacking traps, and confounders.
- Design an A/B test for a checkout change. Sample size, metric, and how you avoid p-hacking.
- Your experiment is significant at p=0.04 but the effect is tiny. Ship it? Defend it.
- Conversion looks up 5% in the test, but only on weekends. What's going on and how do you check?
- You ran 20 metrics and one is significant. What's your concern and what do you do?
Metrics & Business
What the interviewer is testing: turning an ambiguous business question into the right metric and analysis.
- Define the single metric you'd use to measure the health of a two-sided marketplace.
- Revenue is up but the CFO is worried. What second-order metric would you check first?
- How would you detect whether a metric jump is real or a logging bug?
Analytics Case
What the interviewer is testing: diagnosing a metric movement from data, structured and pressure-tested.
- Daily active users dropped 8% week over week. Diagnose it from data, step by step.
- A key funnel step's conversion fell only for Android users in India. Find the cause.
Behavioral
What the interviewer is testing: influencing a decision with data, and a time the data was ambiguous.
- Tell me about a time you shipped something the data later proved was wrong. What did you do?
- Describe a decision where you disagreed with your director and had to defend your call.
- Tell me about the hardest prioritization trade-off you personally owned.
Can you answer these out loud, under follow-up pressure?
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