Calculate variance for A/B test results

Last updated: March 3, 2026

Quick Overview

Given the following scenario about revenue per session, calculate the the p-value.

Jane Street
Statistics & Math
Data Scientist
Jane Street
March 3, 2026
Data Scientist
Onsite
Statistics & Math
Medium

19

6

4,534 solved


Given the following scenario about revenue per session, calculate the the p-value.

Statistics questions at Jane Street test your ability to reason quantitatively and design rigorous experiments. This Onsite question evaluates your understanding of statistical inference and its application to business decisions.

What the Interviewer Expects
  • Set up the problem formally with proper notation
  • Apply the correct statistical test with clear justification
  • Interpret results with appropriate caveats and confidence levels
  • Discuss practical significance vs statistical significance
  • Identify potential confounders and how to address them
Key Topics to Cover
Causal inference basics
Central Limit Theorem
Hypothesis testing (H0, H1, p-values)
Regression analysis
Confidence intervals and significance levels
Power analysis and sample size calculation
How to Approach This
  1. Define your hypotheses (H0 and H1) clearly before performing any test.
  2. Calculate required sample size BEFORE running an experiment, using power analysis.
  3. Remember the Central Limit Theorem: sample means become approximately normal with large n.
  4. Watch for Simpson's paradox. Always segment data by key dimensions.
  5. Distinguish between statistical significance and practical significance.
Possible Follow-up Questions
  • What alternative statistical method could you use here?
  • What assumptions does this test make, and how would you validate them?
  • How would you explain this result to a non-technical audience?
  • How would you handle multiple comparisons?
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Sample Answer
Setting Up the Problem

Start by formalizing the problem: 1. **Define the hypotheses**: H0 (null hypothesis) and H1 (alternative). Be precise about what you're testing. 2. ...

Solution Approach

**Compute the test statistic**: Apply the appropriate formula using the sample data. **Find the p-value**: The probability of observing a result this...


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