Calculate probability for A/B test results

Last updated: October 18, 2025

Quick Overview

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

Google
Statistics & Math
Data Scientist
Google
October 18, 2025
Data Scientist
Technical Screen
Statistics & Math
Easy

279

5

167 solved


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

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

What the Interviewer Expects
  • State the correct formula or theorem with clear definitions
  • Apply the concept to the given scenario step by step
  • Interpret the result in plain language
  • Identify assumptions and when they might be violated
Key Topics to Cover
Power analysis and sample size calculation
Conditional probability and Bayes theorem
Confidence intervals and significance levels
Multiple testing correction (Bonferroni, FDR)
Causal inference basics
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 assumptions does this test make, and how would you validate them?
  • What alternative statistical method could you use here?
  • What if the sample size is very small?
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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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