Evaluate emoji reactions launch

A messaging app is preparing to launch an emoji reaction capability: a user can press and hold a message for 5 seconds to attach an emoji, rather than replying with text. You are the data scientist assigned to support the release. Explain how you would determine whether the feature succeeds, how you would measure its effect, and how you would communicate outcomes to C-level leaders. Your response should address:

1. Product objective: Which user need does this feature address, and what hypotheses would you evaluate?
2. Success metrics: Lay out a metric hierarchy consisting of:
   • one primary success metric,
   • early adoption or engagement metrics,
   • downstream product metrics,
   • guardrail metrics.
3. Experiment design: State whether you would use an A/B test, a staged rollout, or another approach. Be specific about:
   • the randomization unit,
   • network or interference effects among participants in the same conversation,
   • which events or logging are required,
   • the analysis window.
4. Risks and tradeoffs: Cover possible downsides, such as reactions replacing text replies, accidental long-presses, notification overload, a slower messaging experience, or differing effects across user segments.
5. Executive reporting: If the launch had to be summarized for the CEO or other senior stakeholders, what would you share, how would you present the business impact, and what action would you recommend? Assume the company values both user engagement and healthy communication quality, not merely feature usage volume. Overview: This question tests skills in product analytics, experimentation design, metric hierarchy definition, causal inference for social and messaging features, and executive-level communication.