A Type I error blocks a real invoice; a Type II error delivers the phishing email. Which one costs the customer more decides where you set the threshold. The spam-filter framing, the precision/recall mapping, and the asymmetric-cost call interviewers want.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
A Type I error blocks a real invoice; a Type II error delivers the phishing email. Which one costs the customer more decides where you set the threshold. The spam-filter framing, the precision/recall mapping, and the asymmetric-cost call interviewers want.
The screen is whether the candidate keeps Type I (false positive) and Type II (false negative) straight AND maps them to a real business cost rather than reciting definitions. The strong move is to connect Type I to precision, Type II to recall, and then make the asymmetric-cost call (in spam, a false positive that quarantines a legitimate contract is usually worse than letting one spam through). The reserved follow-up: 'so which way do you tune the threshold for this customer': they want a defended decision, not 'it depends.'
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