Calculate variance for A/B test results
Last updated: May 17, 2026
Quick Overview
Given the following scenario about user conversion, calculate the the sample size needed.
JPMorgan
May 17, 2026105
6
4,988 solved
Given the following scenario about user conversion, calculate the the sample size needed.
Statistics questions at JPMorgan test your ability to reason quantitatively and design rigorous experiments. This Phone Screen 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
How to Approach This
- Define your hypotheses (H0 and H1) clearly before performing any test.
- Calculate required sample size BEFORE running an experiment, using power analysis.
- Remember the Central Limit Theorem: sample means become approximately normal with large n.
- Watch for Simpson's paradox. Always segment data by key dimensions.
- Distinguish between statistical significance and practical significance.
Possible Follow-up Questions
- How would you design a follow-up experiment based on these results?
- How would you explain this result to a non-technical audience?
- What if the sample size is very small?
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Problem Formulation
To calculate the sample size needed for an A/B test evaluating user conversion rates, we need to set up the problem using relevant statistical notation. Let be the conversion rate for group ...
Solution Approach
- Determine the expected conversion rates: Assume from historical data that (10% conversion for control) and we want to detect an increase to (15% for treatment)...
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