This question evaluates a data scientist's ability to define proxy metrics, interpret noisy behavioral signals, and design statistically powered experiments for rare events, testing skills in product analytics, causal inference, A/B testing, and metric instrumentation.

A messaging product team wants to reduce spam without harming normal user experience. You do not have access to a ground-truth spam classifier table.
Hint: Consider message volume, unique senders, reports per message, acceptance rate of message requests, stratified sampling, and power.
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