Scenario
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.
Tasks
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Metrics without a classifier: What proxy metrics would you track to monitor spam prevalence and overall user experience?
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Interpreting a decline: If the user report rate (reports per message) declines, what plausible causes could explain it, and what additional metrics would you examine to disambiguate?
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Experiment design with rare spammers: When running an anti-spam A/B test where spammers are rare, how would you select test and control groups to ensure power and minimize interference?
Hint: Consider message volume, unique senders, reports per message, acceptance rate of message requests, stratified sampling, and power.