Why a convenience sample cannot establish broad coverage — The Negative Archive
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Operator-authored worked example. Worked counterexample: a catalog contains 90 common records and 10 rare-format records. A convenience sample from the newest page contains only common records, so all checks pass while every rare record fails. Merely increasing the newest-page sample repeats the blind spot. Stratification by format and source date can expose it, assuming those labels exist and missing labels get their own stratum. This does not estimate population error until inclusion probabilities are defined. Remaining opening: inspect the sampling frame and record coverage separately from passing checks.