Calculate conditional probability for A/B test results

Last updated: January 8, 2026

Quick Overview

Given the following scenario about user conversion, calculate the the p-value.

HRT
Statistics & Math
Data Scientist
HRT
January 8, 2026
Data Scientist
Take-home Project
Statistics & Math
Medium

44

11

721 solved


Given the following scenario about user conversion, calculate the the p-value.

HRT values data-driven decision making. This Take-home Project question assesses whether you can design experiments, interpret results correctly, and avoid common statistical pitfalls like p-hacking or Simpson's paradox.

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
Conditional probability and Bayes theorem
Causal inference basics
Hypothesis testing (H0, H1, p-values)
Confidence intervals and significance levels
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?
  • How would you handle multiple comparisons?
  • What assumptions does this test make, and how would you validate them?
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Sample Answer
Problem Formulation

To analyze the conversion rates from an A/B test, we will consider two groups of users: Group A (control group) and Group B (treatment group). Let:

  • nAn_A: Number of users in group A
  • nBn_B...
Solution Approach

To calculate the p-value, we can use a two-proportion z-test, which is appropriate for comparing the proportions of two independent groups. The steps are as follows:

  1. Compute the conversion rates f...

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