{"id":1467,"slug":"clubcard-data-quality-multiple-users-one-card","title":"Clubcard data-quality lesson — multiple users on one card produced false positives in mining (the \"garbage in\" warning from the best-documented winner)","kind":"reference","scope":"business","status":"current","audiences":["kevin","smb-owner","candid-team"],"topics":["data-pipeline-maintenance","accuracy-risk-published-data","customer-retention"],"reference_body":"**Claim.** Even in the best-documented loyalty-card win, data-quality failures bit the analytics: multiple distinct shoppers using one Clubcard produced false positives in segmentation and propensity mining.\n\n**Source.** mugleston.co.uk summary of Humby et al., *Scoring Points* (2004), accessed 2026-06-21.\n\n**Confidence.** Verified — documented in the participant-authored book itself; a candid acknowledgement, not an external criticism.\n\n**Caveats.** Documented as anecdote rather than measured error-rate; the precise size of the bias is not stated.\n\n**Implication / use.** Concrete instantiation of the \"garbage in\" principle for any information-edge argument. If it happened to Tesco at Clubcard's analytical sophistication, expect it for any SMB. Supports [[rule-three-thresholds-before-claiming-information-edge]] (clean data is the second of three thresholds).","rationale_body":null,"metadata":null,"links":{"outgoing":[{"slug":"research-brief-information-asymmetry-decision-edge-june-2026","title":"Research notes (capture-layer): the affirmative, inward decision-edge case for data intelligence — information asymmetry applied to pricing, demand, risk, retention, targeting (June 2026)","kind":"research-notes","scope":"business","link_type":"depends-on"},{"slug":"tesco-clubcard-1994-trial-9-stores-50m-tx","title":"Tesco Clubcard 1994 trial — 9-14 stores over 3 months, >50 million transactions; dunnhumby analysed ~10pct sample","kind":"reference","scope":"business","link_type":"relates-to"}],"incoming":[{"slug":"rule-three-thresholds-before-claiming-information-edge","title":"Rule: three thresholds before claiming an information edge — volume to clear noise, clean data, an actual decision someone will act on (and timeliness before commoditisation)","kind":"rule","scope":"business","link_type":"depends-on"}]},"created_at":"2026-06-21T01:14:48.735Z","updated_at":"2026-06-21T01:14:48.735Z"}