2-1.3 Measuring agreement and disagreement.

Figure 1 — Record ComparisonWe measure three parameters to get at matching. Figure 1 diagrams the three results that may come about when record linkage compares the values in corresponding fields of two records. It depends on the field being compared, but in the many cases when the values in the corresponding fields agree, the records are more likely matched than not. (NB: The values must be distinctive.) Full agreement means that the form of the data (and in this case probably also the meaning, i.e., what it refers to in the real world) is identical. Each field whose values agree contributes a certain probability in favor of linkage and each field that disagrees contributes a certain probability against linkage. One might compare the situation to members of a committee who each register a vote, either for or against linkage. It is also possible to abstain. This is the case where there are no data in the field — it can neither agree nor disagree. Actually the analogy should be more like the votes of shareholders in a company, since one field may count more heavily than another. (NB: This analogy also fails when we examine all the ways in which our measures might contribute to the strength of a vote. Sometimes a vote may be stronger against than the corresponding vote in favor could be, and vice versa.)

Probabilistic Record Linkage Principle of Comparison