How do you design an A/B experiment?

You have an interview on your agenda titled **“Experiment Design.”** You are asked to design an online experiment (A/B test) for a product change. Describe, step-by-step: - The **goal** and **hypothesis**. - Primary/secondary **metrics** and guardrails. - **Unit of randomization** and how to avoid interference. - **Sample size / power** considerations (what inputs you need). - How you would handle **biases** (selection effects, novelty, seasonality, logging issues). - Decision rules, segmentation, and how you would interpret ambiguous results.