Longform data analysis article arguing every “dataset” is actually three: Observed (captured rows), Missing (what should exist but doesn’t), and Excluded (what filters/joins/dropna removed). Includes dataset accounting, join-loss and missingness audits, segmentation checks, and practical templates to prevent biased KPIs and wrong conclusions.
data-science analytics metrics best-practices instrumentation data-engineering dashboards experimentation data-analysis missing-data missingness joins measurement observability data-quality cohort-analysis sampling-bias selection-bias denominators survivorship-bias
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Updated
Feb 16, 2026