Every person who is registered with a General Practitioner (GP) in Scotland is allocated a 10-digit unique patient identifying number called a Community Health Index (CHI) number. The CHI database contains additional demographic information such as patient's address (including postal code), GP registered with, and date of death (if applicable). For practical purposes, the entire Tayside population is registered with a GP and thus appears in the central computerised records of the Community Health Master Patient Index. Once patients are allocated a CHI number it is never re-allocated so record-linkage of medical data over a large number of years is possible.
The CHI number is used as the patient identifier for all healthcare activities in primary and secondary care in Tayside. The patient-specific number allows for efficient linkage of records of patient activity and outcome.
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