Interpret a statistically significant lift of 2% from an experiment
Last updated: February 24, 2026
Quick Overview
An experiment shows conflicting results. What conclusions can you draw? What are the caveats?
Plaid
February 24, 2026126
5
2,026 solved
An experiment shows conflicting results. What conclusions can you draw? What are the caveats?
This statistics question from Plaid's Take-home Project tests your ability to apply mathematical reasoning to practical problems. The interviewer expects precise definitions, correct methodology, and awareness of assumptions and limitations.
What the Interviewer Expects
- Derive results from first principles when needed
- Handle complex scenarios with multiple interacting variables
- Design experiments that account for real-world complications
- Discuss advanced topics: Bayesian methods, causal inference, resampling
- Connect statistical concepts to business decision-making
- Identify subtle errors in reasoning (Simpson's paradox, survivorship bias)
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
- What if the sample size is very small?
- What alternative statistical method could you use here?
- How would you explain this result to a non-technical audience?
- How would you design a follow-up experiment based on these results?
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Problem Formulation
To analyze the statistically significant lift of 2% from an experiment conducted by Plaid, we first need to frame our problem statistically. Let’s denote the conversion rate of the control group as (...
Solution Approach
- Hypothesis Testing: Define null hypothesis and alternative hypothesis .
- Calculate Sample Size: Ensure that the sample size was sufficient to det...
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