Balance of Arms
A hard SQL mock interview question on DataDriven, with an AI interviewer who asks follow-up questions and a hire or no-hire decision at the end.
- Domain
- SQL
- Difficulty
- hard
- Seniority
- L4
Interview Prompt
Before readout, an experimentation platform checks that each test's arms are balanced: for each experiment, find the unique users in control, the unique users in treatment, and the treatment-to-control ratio. Leave the ratio empty for any experiment whose control and holdout arms drew the same number of unique users, since those splits get reviewed on a separate track.
Summary
Every test has two sides. Count who actually landed on each.
How This Interview Works
- Read the vague prompt (just like a real interview)
- Ask clarifying questions to the AI interviewer
- Write and run your SQL against a real database
- Answer the interviewer's follow-up questions, then get a hire or no-hire decision