Design an A/B test for a new checkout flow

Last updated: January 31, 2026

Quick Overview

Design an experiment to test the impact of a redesigned homepage. Include sample size calculation, metrics, and analysis plan.

Twitter/X

Statistics & Math

Data Scientist

Twitter/X

January 31, 2026

Data Scientist

Phone Screen

Statistics & Math

Medium

4,859 solved

Design an experiment to test the impact of a redesigned homepage. Include sample size calculation, metrics, and analysis plan.

Twitter/X values data-driven decision making. This Phone Screen 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

Causal inference basics

Regression analysis

Probability distributions

Central Limit Theorem

Bayesian vs frequentist inference

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?
What if the sample size is very small?
How would you handle multiple comparisons?

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Sample Answer

Problem Formulation

To design an A/B test for the new checkout flow on Twitter/X, we need to establish the following:

Hypotheses:
- Null Hypothesis (H0): The redesigned homepage has no effect on the conver...

Solution Approach

Calculate the z-scores:
- $Z_{\alpha/2} = 1.96$
- $Z_{\beta} = 0.84$
Calculate the proportions:
- $p_1 = 0.05$ (baseline)
- $p_2 = 0.07$ (expected)
- ...

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Twitter/X Data Scientist Interview Guide

Interview process, tips, and preparation timeline