--- title: "Fellegi–Sunter" summary: "Fellegi–Sunter is the 1969 statistical framework for record linkage that scores a candidate pair as a log-likelihood ratio of field agreements and splits the result into three regions: accept, reject, and refer for review." canonical_url: https://entitybind.com/glossary/fellegi-sunter last_updated: 2026-10-15 copy: full --- # Fellegi–Sunter > Fellegi–Sunter is the 1969 statistical framework for record linkage that scores a candidate pair as a log-likelihood ratio of field agreements and splits the result into three regions: accept, reject, and refer for review. Canonical page: https://entitybind.com/glossary/fellegi-sunter Last updated: 2026-10-15 Glossary · Matching methods ## How to read this The definition as the field writes it comes first, weaknesses and all. What Entity Bind does about it comes last, in its own paragraph, so you can take one without the other. [Filed under matching methods](https://entitybind.com/glossary#matching). By [James Rooney](https://entitybind.com/about), founder of Entity Bind · Last revised 15 October 2026 ## What Fellegi–Sunter means Ivan Fellegi and Alan Sunter's paper '[A Theory for Record Linkage](https://doi.org/10.1080/01621459.1969.10501049)' set out the decision-theoretic basis the field still uses. Each candidate pair is treated as coming from either the matched population M or the unmatched population U. For each comparison field, two conditional probabilities are estimated: the m-probability, that the field agrees given the pair is a true match, and the u-probability, that it agrees by chance given the pair is not. The ratio of those probabilities, in logs, is the field's contribution to the score, and the contributions sum. The result is the paper's most quoted contribution: the optimal decision rule at fixed error rates is a three-region policy. Above an upper threshold, link automatically; below a lower threshold, reject automatically; between them, refer to clerical review. Fellegi and Sunter proved this minimises the size of the review region for a given pair of error rates, which is the reason the shape persists — the middle region is the expensive one, and no policy at those error rates makes it smaller. The framework's assumption is conditional independence between comparison fields, which is usually false: name agreement and address agreement are correlated. Practitioners handle it by modelling dependencies explicitly, by fitting weights discriminatively, or by accepting the bias and choosing thresholds empirically. Entity Bind's scorer is Fellegi–Sunter in shape — three regions, accept, reject and a borderline band — with the weights fitted by regression rather than estimated by expectation-maximisation. The borderline band is what escalates to LLM adjudication and then to agentic research, so the review region is worked rather than merely queued. ### Source - [Fellegi and Sunter (1969), “A Theory for Record Linkage”, Journal of the American Statistical Association 64(328), 1183–1210](https://doi.org/10.1080/01621459.1969.10501049): The paper behind the three-region rule and the m and u probabilities. Its optimality result holds under the model's assumptions, conditional independence between fields among them, which real company data usually breaks. ## Where this shows up in Entity Bind Three pages where this term stops being vocabulary and starts changing an answer, a payload or a price. - [Fellegi-Sunter explained, with worked arithmetic](https://entitybind.com/guides/fellegi-sunter-explained): The Fellegi-Sunter model, published in 1969, is the framework almost every probabilistic matcher is a variation on. Its idea is simple and still correct: for each field… - [The accuracy method](https://entitybind.com/accuracy): Every published rate with the population it was measured over, its interval and its fixture — including the input shapes that fail. - [Compared with Splink](https://entitybind.com/compare/splink): The open-source library most teams reach for first, which learns how much each agreeing field is worth — the Fellegi–Sunter model — and what it does better than we do. The fastest way past a definition is a file: which of your rows are the same company, which of your existing matches we would not have made, and what we could not decide. [Start free →](https://app.entitybind.com/app?signup=1) ## The terms next to this one Each with its own sentence, because the next question is usually about the word beside this one. - [m-probability](https://entitybind.com/glossary/m-probability): The m-probability of a comparison field is the probability that the field agrees given that the pair really is a match — in effect, one minus the rate at which that field is wrong, missing or mistyped in true matches. - [u-probability](https://entitybind.com/glossary/u-probability): The u-probability of a comparison field is the probability that the field agrees by chance given that the pair is not a match — a measure of how common a value is, and therefore of how little an agreement proves. - [Match weight](https://entitybind.com/glossary/match-weight): A match weight is the log-scaled contribution one comparison makes to a pair's score, positive when agreement is evidence of a match and negative when disagreement is evidence against. - [Probabilistic matching](https://entitybind.com/glossary/probabilistic-matching): Probabilistic matching scores a candidate pair by weighing the agreement and disagreement of several fields into a single number, then applies thresholds to that number rather than to any one field. - [Review queue](https://entitybind.com/glossary/review-queue): A review queue is where records the system refused to decide are held for a human, and the quality of a resolver is largely determined by how small, how well-evidenced and how accountable that queue is. - [Record linkage](https://entitybind.com/glossary/record-linkage): Record linkage is the classical statistical name for joining records that refer to the same entity across two or more files with no shared key. ## The other 12 terms on this shelf How two records are compared and how the comparison is made cheap enough to run. Blocking, deterministic rules, probabilistic scoring, string distance. - [Normalisation](https://entitybind.com/glossary/normalisation) - [Transliteration](https://entitybind.com/glossary/transliteration) - [Blocking](https://entitybind.com/glossary/blocking) - [Candidate generation](https://entitybind.com/glossary/candidate-generation) - [Deterministic matching](https://entitybind.com/glossary/deterministic-matching) - [Probabilistic matching](https://entitybind.com/glossary/probabilistic-matching) - [m-probability](https://entitybind.com/glossary/m-probability) - [u-probability](https://entitybind.com/glossary/u-probability) - [Match weight](https://entitybind.com/glossary/match-weight) - [Fuzzy matching](https://entitybind.com/glossary/fuzzy-matching) - [Edit distance](https://entitybind.com/glossary/edit-distance) - [Jaro–Winkler](https://entitybind.com/glossary/jaro-winkler) Previous, alphabetically: [False positive](https://entitybind.com/glossary/false-positive) · Next, alphabetically: [First seen](https://entitybind.com/glossary/first-seen) ## Evidence basis Internal fixtures only. The historical 2026-08-29 per-tier recording covers 317 GB companies with identifier-rich arrivals seeding the catalogue first; the context tier includes country and registered-town prose. Its legacy replay has no full-prompt-verified calls and cannot certify current calibration. The September 5 CI reports cover 1,176 labelled pairs and 705 records over 250 companies using offline stubs. These are not independent customer holdouts or live production validation; the 99% minimum-input product target remains unmet. Scope is company and organisation identity only — not people, vessels, bank-account ownership, sanctions or emissions. Results may not be used for eligibility decisions about individuals, including employment, credit and tenancy. ## Start with your own company records. Create your workspace, verify your email and run your first company file. The Free plan needs no card. Create API keys in your workspace when you need an integration. [Start free](https://app.entitybind.com/app?signup=1) · [All 64 terms](https://entitybind.com/glossary) 300 credits. No card. For a guided review of your file, explore [the Merge Safety Sprint](https://entitybind.com/audit-pack). --- Entity Bind resolves companies and organisations only. It does not resolve people, vessels, bank-account ownership, sanctions exposure, emissions or geolocation, and its results may not be used for eligibility decisions about individuals, including employment, credit and tenancy. This is the Markdown copy of https://entitybind.com/glossary/fellegi-sunter, assembled from the same data the page renders and carrying every sentence, table row, figure and question the page's main content carries. The HTML page is canonical; it adds the layout, the navigation and the interactive parts (the ask panel, the forms), which a copy can name but not run. Every page on the site, with a line on each: https://entitybind.com/llms.txt.