Calculate expected value for coin flips
Last updated: May 29, 2026
Quick Overview
Given the following scenario about user conversion, calculate the the sample size needed.
Splunk
May 29, 20260
5
2,802 solved
Given the following scenario about user conversion, calculate the the sample size needed.
Splunk asks this during the Take-home Project to assess your experimentation skills. They want to see how you define success metrics, design controlled experiments, and interpret results with appropriate statistical rigor.
What the Interviewer Expects
- Define clear success metrics aligned with business goals
- Propose a basic experimental design with control and treatment groups
- Interpret results correctly and draw reasonable conclusions
- Identify obvious confounding variables
Key Topics to Cover
How to Approach This
- Define success metrics carefully. A good metric is measurable, actionable, and aligned with business goals.
- Run experiments long enough to account for novelty effects and weekly seasonality.
- Use funnel analysis to identify where users drop off for maximum optimization impact.
- Segment results by key dimensions (platform, country, user cohort) to catch hidden patterns.
- Consider network effects and interference between treatment and control groups.
Possible Follow-up Questions
- What if the experiment shows a positive short-term effect but you suspect a negative long-term impact?
- How would you handle seasonality in your experiment?
- How would you handle an experiment where the control and treatment groups are different sizes?
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Browse Analytics QuestionsSample Answer
Problem Setup
To calculate the expected sample size for a coin flip experiment aimed at assessing user conversion at Splunk, we first need to establish the analytical question: "What sample size is required to dete...
Methodology
We will use the formula for calculating sample size in a two-proportion Z-test because we are comparing two independent groups (control vs. treatment). The formula is:
[ n = \frac{(Z_{\alpha/2} + Z...
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