Calculate variance for coin flips
Last updated: April 22, 2026
Quick Overview
Given the following scenario about revenue per session, calculate the the p-value.
HubSpot
April 22, 202612
6
1,178 solved
Given the following scenario about revenue per session, calculate the the p-value.
HubSpot asks this during the Phone Screen 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
- Design a rigorous experiment with proper randomization and sample size calculation
- Define primary and guardrail metrics with clear rationale
- Address novelty effects, network effects, and interference
- Segment results appropriately and identify heterogeneous treatment effects
- Propose follow-up analyses when results are ambiguous
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?
- What would you do if a stakeholder wants to end the experiment early because initial results look good?
- What if you discover a bug in the logging during the experiment?
- How would you handle seasonality in your experiment?
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Browse Analytics QuestionsSample Answer
Problem Setup
To calculate the p-value for the variance in revenue per session from coin flips, we first need to frame the analytical question: "Is there a significant difference in revenue generated from two diffe...
Methodology
For this problem, we will utilize a two-sample F-test to compare the variances of revenue per session between the two groups generated by our coin flips. The null hypothesis (H0) is that the variances...
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