## Product / DS Case: Group Calls for Messenger Groups Messenger has **Groups** but does **not** currently support **group calls**. You are evaluating whether to build and launch a group call feature. Answer the following in a product-sense + data-science way: 1) **User need / problem validation** - How would you determine whether users actually need group calls (vs. alternatives like group chat, voice notes, 1:1 calls, or external apps)? - What data and qualitative signals would you use? 2) **Choosing “group size” for the feature** - How would you decide what group sizes to support (e.g., max participants: 4, 8, 16, …)? - What are the tradeoffs (user value, technical cost, quality/reliability, abuse/spam, discoverability)? 3) **Measuring success** Propose: - a primary success metric (or a small set), - diagnostic metrics, - guardrail metrics. Explain why. 4) **Experiment design under interference / network effects** Because users are connected in groups, outcomes may spill over between treated and control users. - If you randomize at a **cluster level** (e.g., groups or user clusters), how do you: - define clusters, - avoid clusters that are still connected (spillover), or clusters that are too large, - analyze the experiment correctly? 5) **A/B test and tradeoffs** - Propose an A/B test plan (unit of randomization, duration, eligibility, rollout). - Discuss key tradeoffs and what could go wrong (e.g., novelty effects, seasonality, infra constraints, measurement gaps).