~ Paupers of the Cleobury Mortimer Union ~
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Nominal record linkage
As the records are created and added to the database, a separate exercise is done to try to identify individuals in different entries who may be the same individual. For example, where several birth records are shown with a "John and Mary Smith" as parents, they may be the same John and Mary Smith in each case, but we cannot be certain.
The records are examined and where several criteria are met, an entry is made in a different table to link the name entries together. The original records are left unchanged and show different person-ids. Two categories are used: probably the same person and possibly the same person. So, in the example of John and Mary Smith, if the baptism entries show the same parents and are within a set number of years of each other, an entry is created to show that one John or Mary Smith is probably the same as another.
In the census records, people are linked if they share the same name and are 9-11 years older from one census to the next (age was an inexact attribute during the 18C and 19C).
Where names are very similar but spelt differently, or the linkage is uncertain, but possible, the link is marked as possibly the same.
When retrieving records, the person-id is looked up in the linkage table and additional person records are retrieved using any chain of linkages found.
Occasionally, it is fairly obvious that one person is the same as another. For example, multiple types of source document at the same date with the same name - eg a baptism record and a bastardy bond, where the name is the only instance at the time. In these cases, the source is recorded with the same person-id. No linkage is necessary.
Record linkage is a slow process and is an ongoing process. It is not accurate and may well miss obvious links.