Marketplace Analytics Case: "Similar Listings You May Like" Notifications

Context

You work on a marketplace where buyers browse and purchase listings. The team is considering a new notification feature (push/email/in-app) that alerts users when new listings similar to items they've viewed or saved become available. The goal is to increase user engagement and conversion without causing notification fatigue or harming overall marketplace health.

Tasks

1. Decision framework: How would you decide whether introducing this notification feature is a good idea? State your hypotheses, expected user/business value, risks, and prerequisites.
2. Experiment design: Propose an A/B test to evaluate the feature. Specify unit of randomization, eligibility, randomization scheme, sample size/power, duration, attribution windows, and a roll-out plan (ramp/holdouts).
3. Success criteria: Define and justify primary, secondary, and guardrail metrics (e.g., CTR, conversion, retention, user satisfaction), including precise metric definitions and evaluation windows.